Secondary Service Connection Explained

Under 38 CFR 3.310, a disability that is proximately caused by or proximately aggravated by a service-connected disease or injury shall be service-connected. This means if an already service-connected condition causes a new, distinct medical issue, the new issue can also be rated and compensated.

Secondary service connection is not automatic. Association between conditions does not by itself establish secondary service connection. The evidence must support causation or aggravation in the individual claim. The veteran must provide medical evidence, typically a nexus letter or an independent medical opinion, demonstrating that the secondary condition is 'at least as likely as not' caused or aggravated by the primary condition. A mere diagnosis is not enough without that medical link.

If a veteran had a non-service-connected condition, and a service-connected condition makes it permanently worse (beyond its natural progression), the veteran may claim secondary service connection for the degree of aggravation. This requires baseline medical evidence showing the severity before the aggravation occurred.

Once secondary service connection is established, the secondary condition is rated according to its own diagnostic code and severity criteria in the VA rating schedule, exactly as if it were a primary condition. The rating is then combined with the veteran's other ratings using standard VA math.