Secondary service connection claiming conditions your service-connected disability caused or made worse

Secondary service connection is how VA pays for a condition that a service-connected disability caused or made worse. VA grants it in two ways under 38 CFR 3.310: the condition was caused by a service-connected disability, or it was aggravated by one, meaning it would be less severe but for that disability. Either way, the new condition gets its own rating, which combines with the ratings you already have.

What the claim needs Common secondary conditions

Written and reviewed by Landon · Updated October 6, 2026 · Board data 2021 to 2026

53.7%of secondary service connection rulings the Board granted or denied were grants (76,344)
99.4%granted when the Board credited a favorable medical opinion
22.9%granted with no medical opinion in the file
116secondary pairs checked by hand before any figure is shown

Board figures: Claim Raven's analysis of Board of Veterans' Appeals service connection rulings, 2021 to 2026. The first three count only rulings the Board granted or denied, because it weighs medical opinions only then; compare them with that group's own rate, not with a rate that counts remands.

How secondary service connection works

The rule is 38 CFR 3.310. Paragraph (a) says a disability "which is proximately due to or the result of a service-connected disease or injury shall be service connected." Paragraph (b) covers aggravation. VA's claims manual, M21-1 V.ii.2.D, tells raters how to apply both.

Caused by

VA's manual says a secondary disability qualifies when it is "the result of, or would not have occurred but for," a service-connected disability. The medical opinion has to find that link at least as likely as not. Two details widen this route.

Treatment counts. A condition caused by treatment for a service-connected condition can be claimed secondary to it. In Spicer v. McDonough, the Federal Circuit pointed to a case where VA paid for tinnitus caused by medicine for tuberculosis that began in service.
Timing does not have to follow your rating. The manual says "the primary disability need not be SC, or even diagnosed, at the time the secondary disability is incurred" (SC means service connected). Its example is a rotator cuff torn in a fall caused by early, undiagnosed radiculopathy.

Aggravated by

Aggravation covers a condition with its own cause, often one you already had, that your service-connected disability made worse. A medical opinion puts it this way: the condition is aggravated by the veteran's service-connected back condition, meaning it would be less severe but for the back condition. VA rewrote its manual's aggravation rules in May 2026, covered in the Spicer section below.

The baseline

The baseline is how severe the other condition was before your service-connected disability started to worsen it. VA pays only for the part above it: raters find the rating the baseline and the current level would each get, then subtract (M21-1 V.ii.2.D.1.g). If the baseline would rate 10 percent and the current level rates 30 percent, VA assigns 20 percent. A "caused by" claim has no baseline step; VA rates the whole condition.

Secondary conditions the rule presumes

Section 3.310 presumes the link in two situations: heart or other cardiovascular disease after a service-connected leg amputation at or above the knee (or both legs at or above the ankles), and, after a service-connected TBI, Parkinsonism, unprovoked seizures, certain dementias, hormone-deficiency diseases and depression within set severity and time limits. Claims outside those limits follow the general rules.

What a secondary claim needs

The Board states the test as three elements: a current disability, a service-connected disability, and nexus evidence, "generally medical," connecting the two (A25000331, January 2, 2025). In practice, your file needs four things.

A current diagnosis of the secondary condition, made with the usual test, such as a sleep study for sleep apnea.
A service-connected condition to link it to. If the first condition is not service connected yet, claim both together. The secondary claim can be granted only if the first one is.
A medical opinion with reasoning that answers two questions separately: did the service-connected condition cause the new one, and did it make it worse? The Board weighs an opinion mostly by its reasoning (A25000430).
Your account of the timeline: when symptoms began, and how the service-connected condition changed your activity, sleep or medication. A personal statement and buddy letters put that on record. They support the medical opinion; they do not replace it.

If VA orders a C&P exam, the C&P exam prep tool covers what the examiner should address. The Board figures below compare how medical opinions fared in secondary claims and in direct claims.

What the Board did with medical opinions: secondary and direct claims

Service connection rulings the Board granted or denied, 2021 to 2026, by what it credited among the medical opinions. The share is granted. Across all of them, secondary claims were granted 53.7% of the time (76,344 rulings) and direct claims 46.1% (217,271).

Favorable opinion credited32,973 secondary, 52,251 direct 99.4%vs 99.1%
VA opinion set aside7,016 secondary, 36,645 direct 70.4%vs 84.3%
Opinion against claim22,904 secondary, 67,481 direct 1.0%vs 0.5%
No medical opinion13,451 secondary, 60,894 direct 22.9%vs 28.0%

Remands are left out, because the Board weighs the opinions only when it grants or denies, so compare these shares with that group's own rate, not with a rate that counts remands. Associations, not causes: a doctor usually writes a favorable opinion because the facts support it. Source: Claim Raven analysis of Board decisions.

Secondary aggravation after Spicer

The text of 38 CFR 3.310(b) has not changed. It still describes an increase "not due to the natural progress" of the condition, and still tells raters to deduct natural progress. VA no longer applies that part.

In Spicer v. McDonough (Fed. Cir. 2023), medicine for the veteran's service-connected leukemia kept the red blood cell level too low for a scheduled knee replacement, and VA denied secondary service connection for the knees. The Federal Circuit held that "resulting from" in 38 U.S.C. 1110 requires but-for causation, vacated the decision, and held 3.310(b) unlawful to the extent VA used it to reject that theory.

VA changed its manual on May 1, 2026 to follow Spicer. M21-1 V.ii.2.D now says VA "will apply the broader but-for standard and will no longer consider natural progress" when deciding an aggravation claim (NSC means non-service-connected). The rule now works as follows.

The question is but-for. Aggravation covers an increase "that would not have occurred but for the SC disability," or a condition that "would have been less severe but for the SC disability, including where the SC disability has interfered with or impeded treatment" for it.
Natural progress is out, and permanence is not required: "Permanent worsening of an NSC disability by an SC disability is not required."
A baseline is still required. VA sets it from medical evidence created before the aggravation began, or the earliest medical evidence created after it. Your own statements can support it, but the manual says lay evidence "on its own, may not be sufficient."
No baseline means no grant. If none can be set after VA has helped develop the evidence, the aggravation claim "must be denied." VA may not assume a 0 percent baseline.
The rating is the difference, current level minus baseline. If the condition got worse but both levels fall at the same rating, VA still grants service connection at 0 percent.
The exam has to cover it. The examiner must separately state the current severity, answer the but-for question and explain the medical reasoning.

One line to keep separate: a condition that existed before service and got worse during service falls under 38 CFR 3.306, which still asks whether the increase was due to the natural progress of the disease.

Intermediate steps: obesity and medication side effects

Some claims run through a middle step: the service-connected condition causes something that in turn causes the claimed condition.

Obesity as an intermediate step

VA's General Counsel settled this in VAOPGCPREC 1-2017 (January 6, 2017; official PDF in Sources). It held that "Obesity per se is not a 'disability' for purposes of 38 C.F.R. § 3.310," so obesity cannot be service connected or rated by itself, but that it "may be an 'intermediate step'" toward a condition that can be. Using a back disability, obesity and high blood pressure as its example, it set three questions.

Did the service-connected disability cause the veteran to become obese?
If so, was that obesity a substantial factor in causing the claimed condition?
Would the claimed condition not have occurred but for that obesity?

Three yes answers support secondary service connection. In Walsh v. Wilkie, 32 Vet. App. 300 (2020), the Court of Appeals for Veterans Claims added that obesity made worse counts too, finding "no legal basis to recognize a causal relationship but not an aggravating one in these circumstances." The Board must consider that theory when the veteran raises it or the record reasonably raises it, so name the weight-gain theory in your claim.

In January 2025 the Board granted sleep apnea secondary to PTSD with obesity as the intermediate step (A25000430). Two private opinions covered each link: the weight gain was due to PTSD, the sleep apnea was due to the weight gain, and without it the sleep apnea would not have occurred. The Board gave little weight to conclusory VA opinions that never addressed aggravation. Weights from routine visits, medication lists and notes about lost mobility usually carry the middle link; put them on one timeline.

Medication side effects

Medicine taken for a service-connected condition can cause a second condition that is claimed secondary to the first. In February 2025 the Board granted GERD secondary to service-connected knee and foot conditions through NSAID use (A25014545). Records back to 2010 showed NSAIDs for the knee and foot pain, and a VA examiner found the GERD at least as likely as not due to that use. The file needs records showing the medicine was prescribed for the service-connected condition, a diagnosis, and an opinion that addresses dose and timing. See the GERD guide and erectile dysfunction secondary to PTSD.

Chains: when a secondary condition causes another

Once granted, a secondary condition "shall be considered a part of the original condition" (3.310(a)), so it can be the starting point for the next claim. In Spicer, the court described but-for causation as a standard that "encompasses multi-link causal chains," and noted that VA has accepted causation running through several steps.

A common chain starts with a joint. In the same January 2025 decision, the Board granted a low back condition with right leg radiculopathy as proximately due to a service-connected right knee (A25000430). With the back granted, conditions it causes or worsens can be claimed secondary to it (back secondary to knee covers that first link). Chains hold up when each link stands on its own.

Each claimed condition has its own diagnosis, including the middle one.
Each link has its own medical reasoning. An opinion on knee to back says nothing about back to the next condition.
The order is clear. If the middle condition is not service connected yet, claim it with the last one and make sure the opinion covers both steps.
The weakest link decides. If one link is denied, every claim that depends on it fails unless another route supports it.

Nexus letter for a secondary condition

The nexus letter is the medical opinion linking the two conditions. It answers two questions and, for aggravation, measures the change.

What a strong secondary nexus letter does

Names both conditions exactly: the service-connected one with its rating decision, and the claimed one with its diagnosis and date.
Lists the records reviewed, by date.
Answers causation and aggravation separately, each with its own conclusion and reasons. In El-Amin v. Shinseki, 26 Vet. App. 136 (2013), the Court held that an opinion saying one condition did not cause another was not enough to decide whether it aggravated it.
Asks the current aggravation question: would the condition be less severe but for the service-connected condition, including any effect on treatment? It does not ask about natural progress or permanence.
Names the baseline record if it finds aggravation, beside the current severity.
Explains the link in your history: dates, doses, weights and the order things happened. Research supports the reasoning; it is not the reasoning.
Deals with other causes such as age, weight or smoking, and explains why the service-connected condition is still a but-for cause. A condition can have more than one cause.
States the clinician's qualifications and is signed and dated.

Example outline of a secondary nexus letter

This fictional outline follows the NSAID claim above. It shows order and content; the clinician writes the opinion.

Records reviewed: the rating decision for the right knee, pharmacy records for prescription NSAIDs, and the record that diagnosed GERD.
History: when knee pain began, when NSAIDs started, dose and frequency, and when reflux began.
Causation: whether the GERD is at least as likely as not caused by NSAIDs taken for the service-connected knee, with reasoning.
Aggravation: whether the GERD is aggravated by the veteran's service-connected knee condition, meaning it would be less severe but for the knee condition, and if so, the baseline record and current severity.
Other causes considered, such as weight, smoking and other medicines, and why each does or does not change the answer.
Clinician's credentials, signature and date.

Raven Nexus organizes the records and research you choose into a draft your clinician can review, change and sign. See also VA nexus letter examples, and pair pages such as sleep apnea secondary to hypertension and hypertension secondary to PTSD.

Why secondary claims get denied

Most denials trace back to the opinion or the record behind it, and each has a fix.

No current diagnosis. Get the condition diagnosed, then file.
The first condition is not service connected. Claim both together, or win the first one first.
The opinion only addressed "caused by." That is inadequate on aggravation (El-Amin); in January 2025 the Board sent a sleep apnea claim back for exactly that (A25000331). Ask for an opinion that answers both, or submit a private one.
A conclusion without reasons, or "commonly associated" with nothing tied to your history. Get an opinion that applies the reasoning to your dates and records.
No baseline for an aggravation claim. Find the earliest record showing how severe the condition was before, or soon after, the worsening began.
Another cause got the blame, such as weight, age or smoking. Get an opinion that addresses each one.
The middle step was never raised. If the claim runs through weight gain or medication, say so and attach the records.
The examiner used the old aggravation test, natural progress or permanent worsening. Point to M21-1 V.ii.2.D and ask for an opinion on the but-for question.

To compare your options after a denial, use the Appeals Advisor.

How secondary ratings combine

A secondary condition gets its own rating under its own diagnostic code, and VA combines it with your other ratings under 38 CFR 4.25. Combined ratings are not added. VA starts with the largest rating, each smaller one takes its share of what is left, and VA rounds once, at the end, to the nearest 10, with 5 rounding up.

Say you are rated 40 percent for a low back condition, and VA grants radiculopathy of one leg secondary to the back at 20 percent: 40 and 20 combine to 52, which rounds to 50 percent. Later VA grants depression secondary to back pain at 30 percent. Now 40 and 30 combine to 58, and 58 and 20 combine to 66, which rounds to 70 percent.

For an aggravation grant, the number that combines is the difference VA assigned. If the secondary condition is in the opposite arm or leg and both sides are rated at least 10 percent, 38 CFR 4.26 adds a bilateral factor. The VA disability calculator runs the math.

Pyramiding: when VA won't rate the same thing twice

38 CFR 4.14 says "The evaluation of the same disability under various diagnoses is to be avoided," and so is rating "the same manifestation under different diagnoses." A secondary claim adds a rating only when it brings symptoms the first rating does not already count. The common case is mental health: depression or insomnia claimed secondary to service-connected PTSD shares symptoms the PTSD rating already counts, so VA rates the mental health picture once. See insomnia secondary to tinnitus and PTSD secondary conditions.

Secondary conditions and TDIU

Secondary conditions count toward TDIU like any other service-connected condition. For the single-condition thresholds, 38 CFR 4.16(a) treats "disabilities resulting from common etiology or a single accident" as one disability, which can let a primary condition and the conditions it caused count together.

Common VA secondary conditions

Any condition a clinician can link to a service-connected one, with reasoning, can be claimed. These pages list what veterans claim from common starting points.

Pages for single pairs cover the research, rating, C&P exam and nexus letter.

Sleep apnea secondary to PTSD, tinnitus, depression, a back condition or hypertension.
Joints and spine: back secondary to knee, hip secondary to knee, hip secondary to back, back secondary to flat feet.
Heart, kidney and blood sugar: hypertension secondary to PTSD, diabetes secondary to hypertension, kidney disease secondary to hypertension.
Head, ears and sleep: migraines secondary to PTSD, migraines secondary to tinnitus, insomnia secondary to tinnitus, vertigo secondary to tinnitus.
Digestive and urological: GERD secondary to PTSD, IBS secondary to PTSD, erectile dysfunction secondary to PTSD.

If knee pain brought you here, the knee guide covers how VA rates a knee, code by code. The secondary condition finder starts from any condition you already have and lists what veterans claim from it, with the medical questions each one raises.

The Board figures below show the secondary pairs that reach the Board most often and how often each was granted.

The secondary pairs that reach the Board most often

Service connection rulings, 2021 to 2026, on a claim the Board's order wrote as one condition secondary to another. The share is granted out of every decided ruling, remands included.

Sleep Apnea secondary to PTSD4,031 decided 37.7%
Nerve Conditions of the Legs secondary to Lumbar Spine3,387 decided 37.4%
Neuropathy secondary to Diabetes2,707 decided 33.8%
Radiculopathy secondary to Lumbar Spine2,462 decided 43.6%
Nerve Conditions of the Legs secondary to Diabetes1,691 decided 35.1%
Lumbar Spine secondary to Knee1,487 decided 22.5%
Hip secondary to Knee1,284 decided 18.1%
Nerve Conditions of the Arms secondary to Cervical Spine1,148 decided 34.5%
Sleep Apnea secondary to Depression1,132 decided 42.0%
Knee secondary to Lumbar Spine1,129 decided 10.5%

Each pair is shown only after a sample of its Board orders was read by hand and the automatic reading was right at least 85% of the time. Source: Claim Raven analysis of Board decisions.

If you want help deciding which secondary claims your records support, Pathfinder reads your records and guides you through each claim to filing day. A Veterans Service Organization can also file for you at no cost.

Questions veterans ask about secondary service connection

What is the difference between direct and secondary service connection?

A direct claim ties a condition to something that happened during service. A secondary claim ties it to a condition VA has already service connected. In a presumptive claim, the law supplies the link.

Can I claim a secondary condition before the first condition is service connected?

Yes. File both together; the secondary claim can be granted only if the first one is. The secondary condition does not need to have started after the first was service connected or even diagnosed (M21-1 V.ii.2.D.1.b).

How much does a secondary condition add to my VA rating?

Less than its face value, because VA combines ratings instead of adding them. A 30 percent secondary rating on top of a 50 percent rating combines to 65, which rounds up to 70 percent.

Which secondary claims are easiest to win?

None is automatic. The ones that hold up have a clear diagnosis, records that show the order of events, and an opinion that explains the link in your history. The Board figures above show grant rates for common pairs.

Can you get a VA rating for obesity?

No. VAOPGCPREC 1-2017 holds that obesity cannot be service connected or rated on its own. It can be the middle step toward a condition such as high blood pressure or sleep apnea.

Does aggravation have to be permanent?

No. VA's manual says permanent worsening is not required, and since May 1, 2026 VA no longer considers natural progress. It still needs a baseline.

Do I need a nexus letter for a secondary condition?

The link is a medical question, so the claim needs a medical opinion. VA may get one through a C&P exam; a private opinion helps when the VA opinion skips aggravation or gives no reasons.

Sources and method

38 CFR 3.303 (opens in a new tab), 3.306 (opens in a new tab), 3.310 (opens in a new tab), 4.14 (opens in a new tab), 4.16 (opens in a new tab), 4.25 (opens in a new tab) and 4.26 (opens in a new tab), eCFR text as of October 1, 2026, read October 6, 2026.
M21-1, Part V, Subpart ii, Chapter 2, Section D (opens in a new tab), Secondary Service Connection and Aggravation of Non-Service-Connected Disabilities, change date May 1, 2026.
Spicer v. McDonough (opens in a new tab), 61 F.4th 1360 (Fed. Cir. 2023).
El-Amin v. Shinseki (opens in a new tab), 26 Vet. App. 136 (2013).
Walsh v. Wilkie (opens in a new tab), 32 Vet. App. 300 (2020).
VA General Counsel Precedent Opinion 1-2017 (VAOPGCPREC 1-2017), Service Connection Based on Obesity (opens in a new tab), January 6, 2017, official PDF.
Board of Veterans' Appeals decisions, each binding only its own appeal: A25000331 (opens in a new tab) (January 2, 2025, remanded), A25000430 (opens in a new tab) (January 3, 2025, granted) and A25014545 (opens in a new tab) (February 18, 2025, granted).
Board figures on this page: Claim Raven's read of every Board decision from 2021 to 2026 that it holds, and of every decision since 1992 for the longer view.

Cite this page

Claim Raven. Secondary service connection: the rule, aggravation after Spicer and Board outcomes. Board data 2021 to 2026. https://claimraven.com/secondary-service-connection

Claim Raven explains VA rules in plain English so you can work your own claim. It is not legal advice, and Claim Raven is not affiliated with the Department of Veterans Affairs. Board outcomes describe appeals that reached the Board; they don't predict any one claim.