“Presumptive” and “secondary” do not mean automatic. They are different legal routes with different elements, evidence, and effective-date rules. Start by identifying the theory that actually fits the facts, then name that theory in the claim. Claim Raven's secondary-condition checklist and presumptive-condition tool can help you organize questions; they are screens, not eligibility decisions.

Five service-connection paths

  1. Direct service connection. A current disability, an in-service disease, injury, event, or exposure, and a nexus connecting the current disability to that service event. See 38 CFR § 3.303. A post-service diagnosis does not rule out direct service connection if competent evidence connects it to service.
  2. Secondary causation. A current disability is proximately due to a service-connected disability under 38 CFR § 3.310(a). The primary disability must already be service connected (or be granted in a decision that also grants the secondary issue), and a clinician should explain the causal mechanism. A common example is sleep apnea caused by a service-connected upper-airway condition, but “commonly claimed” is not proof.
  3. Secondary aggravation. A service-connected disability worsens a separate condition beyond its natural progression. Under § 3.310(b), VA will not concede aggravation unless the baseline level of severity is established by qualifying medical evidence. VA then compensates only the additional degree attributable to the service-connected condition. The opinion should identify the baseline, the current severity, and the reasoning connecting the two.
  4. Preexisting-condition aggravation. A condition noted before service may be service connected if it was aggravated during service under 38 U.S.C. § 1153 and 38 CFR § 3.306. This is not the same as secondary aggravation after service. The evidence must address the pre-service baseline, in-service worsening, and whether the increase was beyond natural progression. The presumption of soundness can also matter when a condition was not noted at entry; a representative can help select the correct theory.
  5. Presumptive service connection. Congress or VA supplies a service, exposure, timing, or disease presumption. The presumption can remove the need for a separate nexus opinion, but you still generally need a qualifying diagnosis or the exact evidence required by the rule, qualifying service, and a current disability. If the facts fall outside the presumption, direct or TERA evidence may still be available.

Gulf War chronic disabilities

Under 38 U.S.C. § 1117 and 38 CFR § 3.317, a Gulf War undiagnosed-illness claim is the diagnosis exception: objective indications of a chronic disability can qualify even when symptoms cannot be attributed to a known clinical diagnosis. A diagnosed medically unexplained chronic multisymptom illness, or an illness designated by regulation, follows its own requirements. Symptoms must be chronic under the rule, and the record still needs qualifying service, objective indications, and evidence that the disability meets the applicable manifestation and exclusion requirements.

The § 1117 service screen is broader than a shorthand “Iraq or Kuwait” list. The Southwest Asia theater includes Iraq, Kuwait, Saudi Arabia, the neutral zone between Iraq and Saudi Arabia, Bahrain, Qatar, the United Arab Emirates, Oman, the Gulf of Aden, the Gulf of Oman, the Persian Gulf, the Arabian Sea, the Red Sea, and airspace above those locations. Section 1117 also names Afghanistan, Israel, Egypt, Turkey, Syria, and Jordan. Afghanistan service in 1995 may therefore fit the separate § 1117 screen even though it does not satisfy later PACT or 38 CFR § 3.320 date rules. The infectious-disease branch in § 3.317(c) is narrower and has separate locations and manifestation periods; do not substitute the broad chronic-disability list for that branch.

Other presumptions and toxic exposure

Chronic diseases listed in 38 CFR §§ 3.307 and 3.309 can be presumed service connected when they manifest to the required degree within the applicable period. Agent Orange and other herbicide rules use their own service locations and disease list. Camp Lejeune water-contamination rules have a defined period, location, and condition list. The PACT Act chapter separates §§ 1119–1120 and 38 CFR §§ 3.320, 3.320a, and 3.320b from § 1117, because their country and date requirements differ.

The Toxic Exposure Risk Activity (TERA) route under 38 U.S.C. § 1168 is not a blanket presumption. When a claim is based on a covered TERA and there is evidence of a current disability, VA generally must obtain a medical examination and opinion addressing whether the disability is related to the exposure, subject to statutory exceptions. Preserve deployment records, occupational duties, exposure descriptions, and medical literature. A TERA opinion can support direct service connection even when the disease is not on a presumptive list; it does not eliminate the need for a current disability or a reasoned medical explanation. See Chapter 25: TERA and Toxic Exposure Claims.

Build the record for the theory

Use one evidence plan for each theory. Direct claims need the in-service event and nexus. Secondary-causation claims need the primary service-connected condition and a causal explanation. Aggravation claims need a defensible baseline and measurable worsening. Presumptive claims need proof of qualifying service and the rule's diagnosis or manifestation requirements. A nexus letter guide, contemporaneous treatment records, personnel records, DBQs, and credible buddy statements can complement one another, but a conclusory form or a list of conditions is not a substitute for rationale.

Official sources