Secondary Service Connected Conditions

38 CFR § 3.310(a) provides that "disability which is proximately due to or the result of a service-connected disease or injury shall be service connected." This means a veteran can claim a second condition as service-connected if that condition was caused or chronically worsened by an already-rated primary service-connected disability.

The most reliable nexus evidence is a private medical opinion — often called a nexus letter — from a treating physician or independent medical examiner. The opinion must (1) acknowledge the primary service-connected condition, (2) diagnose the secondary condition, and (3) state that the secondary is "at least as likely as not" (50% or greater probability) caused or aggravated by the primary. Treatment records alone are supporting evidence, not a substitute for the nexus opinion.

Yes. Secondary conditions receive their own rating under 38 CFR Part 4 diagnostic codes. The VA then combines all ratings — primary, secondary, and any other service-connected conditions — using the combined ratings formula under 38 CFR § 4.25. Because the formula applies the whole-person concept, the combined rating is always less than a simple sum of individual ratings.

38 CFR § 3.310(a) governs conditions proximately caused by the primary. § 3.310(b) governs aggravation — where the primary condition permanently worsens a pre-existing, non-service-connected disability beyond its natural progression. Both pathways lead to service connection, but the evidence requirements differ: aggravation requires showing the pre-existing condition worsened beyond its natural course, not just that it coexists with the primary.

The effective date for a new secondary claim is generally the date VA receives the claim, or the date of an Intent to File (VA Form 21-0966) submitted within the preceding 12 months. If the VA should have awarded secondary service connection in a prior decision but failed to, a Supplemental Claim or Higher-Level Review may establish an earlier effective date.