What connects a disability to service

Service connection is VA's legal recognition that a current disability is related to military service under some applicable rule. A medical form can document the condition; why it qualifies usually needs different evidence.

Direct

A current disability, something that happened in service, and a connection between them. The record may include service and treatment records, medical reasoning, and firsthand observations. What VA says it needs.

Secondary — and this is where claims go wrong

A disability caused by, or aggravated by, a condition that is already service-connected. 38 C.F.R. §3.310 covers both, in two separate paragraphs, and they ask different things:

• Causation — paragraph (a). Did the service-connected condition bring this one about?
• Aggravation — paragraph (b). Did it make a condition you would have had anyway measurably worse?

An opinion that answers only the first leaves the second untouched. "Condition A did not cause condition B" does not tell anyone whether A made B worse, and claims come back for further development on exactly that gap.

Aggravation also has machinery of its own. The regulation requires a baseline level of severity — established from medical evidence created before the aggravation began, or the earliest evidence showing when it started — and then deducts both that baseline and any worsening attributable to the natural progress of the disease. So "it got worse" is not the finding; "it got worse by more than it would have anyway, measured from this point" is.

Two court decisions limit how far that arithmetic reaches, and both favor veterans:

• VA cannot require that the worsening be permanent. Ward v. Wilkie set aside Board instructions that told examiners it must be, holding that requirement appears in neither the statute nor the regulation.
• VA cannot use paragraph (b) to reject a worsening caused by not being able to get treatment. Spicer v. McDonough held that 38 U.S.C. §1110 reaches "a worsening of functionality — whether through an inability to treat or a more direct, etiological cause," and that §3.310(b) is "unlawful as inconsistent with" §1110 to the extent VA applied it to refuse that theory.

VA has not amended §3.310(b) since 2013, so the text you will find on eCFR is still the text the Federal Circuit limited. Read it knowing that.

Two conditions appearing together, or sharing a risk factor, is not a nexus. That connection needs medical support.

Presumptive

Certain laws and regulations specify qualifying service, exposure, condition and timing, and treat those facts as establishing an element. The PACT Act overview is the starting point for toxic exposure. A presumption is narrow by design — it is not a shortcut for every diagnosis.

After service connection

VA still has to decide the evaluation and the effective date, which are separate questions again. An accredited representative can tell you which theories your particular record supports; this page can only tell you they exist. Find help.

Reviewed October 6, 2026