Some of the most valuable VA claims are for conditions that never happened in service at all. When a service-connected disability causes or worsens another condition, that second condition can itself be service connected. The authority is one regulation: 38 CFR 3.310. Secondary connection is one of four ways the VA connects a condition to service - our service connection overview covers all of them.
What the regulation says
Section 3.310 provides that a disability which is proximately due to or the result of a service-connected disease or injury shall be service connected. It also covers aggravation: when a service-connected condition aggravates a non-service-connected condition, the veteran is compensated for the degree of disability over and above what the condition would have caused on its own.
The evidence elements
A secondary claim mirrors the elements of any claim, with the service-connected condition standing in for the in-service event:
- A current diagnosis of the secondary condition
- An existing service-connected (primary) disability
- Medical evidence linking the secondary condition to the primary one - with a medical explanation of the mechanism
Why the mechanism matters
The linking opinion cannot just assert that one condition led to another. It has to explain how: the physiological pathway, the side effect of treatment, or the altered mechanics. 'PTSD can drive the weight gain and upper airway changes that produce obstructive sleep apnea' is a mechanism. 'The two conditions are related' is not.
This is the element most often missing when secondary claims are denied - the same nexus element that decides direct claims, covered in our guide on what evidence the VA needs.
Common secondary pathways
The VA's rating schedule and the regulation together support many well-established pairings. Sleep apnea secondary to PTSD is one of the most claimed - our PTSD and mental health series covers it in depth. Others include conditions caused by medications for a service-connected disability, and joints damaged by years of compensating for a service-connected knee or back.
Where veterans start
Every case is different, and there is no obligation at any step. When veterans want to understand what their records actually support, these are the two most common starting points:
- Medical records review
A licensed physician reviews your records for a $250 flat fee and identifies which conditions the available evidence may support. The fee is refunded in full if nothing supportable is identified.
- Nexus letter
When the records support one, a licensed provider writes the medical opinion that addresses the link between your condition and your service.
Filing a secondary claim
A secondary condition is claimed the same way as any other disability claim, on the VA's how to file page, but the claim should identify both the new condition and the already service-connected condition it is claimed as secondary to. This tells the VA rater which primary disability the medical evidence needs to be evaluated against.
The VA may schedule a claim exam specifically to address the secondary relationship, and the examiner will typically be asked to state whether the secondary condition is at least as likely as not caused or aggravated by the service-connected condition identified in the claim.
Aggravation claims need a baseline
When a secondary claim is based on aggravation rather than direct causation, 38 CFR 3.310 requires establishing the baseline level of the non-service-connected condition before the aggravation, so the degree of additional disability caused by the service-connected condition can be measured. Medical evidence documenting the condition's severity before and after the aggravating factor is what supports that measurement.
Without a documented baseline, it can be difficult for a rater to separate the natural progression of the condition from the portion attributable to the service-connected disability, which is why aggravation opinions typically address both points explicitly.
Multiple secondary conditions from one primary condition
A single service-connected condition can support more than one secondary claim if the medical evidence shows more than one downstream effect. A service-connected knee condition, for example, might be linked through separate medical opinions to a secondary hip condition from altered gait and to a secondary back condition from compensating for the knee. Each secondary condition still needs its own medical evidence establishing the specific mechanism.
This guide is educational. It summarizes the VA's own published rules and links to the exact sources it relies on. It is not legal or claims advice, and it is not a substitute for an accredited representative, who can advise you about your specific claim. Accredited help is free - search the VA's accreditation database to find a Veterans Service Organization, accredited agent, or attorney.
Frequently asked questions
What is secondary service connection?
It is service connection granted for a disability caused or aggravated by an already service-connected condition, rather than by service directly. It comes from 38 CFR 3.310. Sleep apnea caused by service-connected PTSD is a common example.
What evidence does a secondary claim need?
A current diagnosis of the secondary condition, an already service-connected primary condition, and medical evidence linking the two. The medical opinion has to explain the mechanism - how the primary condition caused or worsened the secondary one.
What does aggravated mean in 38 CFR 3.310?
Aggravation means the service-connected condition made the secondary condition permanently worse beyond its natural progression. The regulation allows service connection for the degree of worsening, and the medical evidence has to support it.