Your service-connected condition doesn’t have to be the only thing you’re compensated for. If it caused something else — or made something else worse — that counts too.
Secondary service connection is the most underused route in the entire claims system, and it doesn’t require proving anything new about your time in service.
Three Routes to Service Connection
| Route | What you have to show | Typical example |
|---|---|---|
| Direct | The condition began in or was caused by service | A back injured in a training accident |
| Presumptive | You served in a qualifying place and time, and have a listed condition | A condition presumed from burn pit exposure |
| Secondary | An existing service-connected condition caused or worsened the new one | Depression that developed from chronic service-connected pain |
The advantage of the secondary route is that the service part is already settled. You aren’t reopening what happened decades ago — you’re connecting today’s condition to a rating you already hold.
Causation vs. Aggravation
The regulation covers two distinct situations, and they’re proven differently.
Causation: a disability proximately due to or the result of a service-connected disease or injury. Once granted, the secondary condition is treated as part of the original condition.
Aggravation: a nonservice-connected condition that got worse because of a service-connected one, beyond its natural progression.
The Baseline Trap in Aggravation Claims
This is where aggravation claims fall apart, and almost no guide explains it.
VA will not concede aggravation unless the baseline level of severity of the nonservice-connected condition is established by medical evidence — created either before the aggravation began, or at the earliest point between onset and the evidence showing the current severity.
Then VA deducts that baseline, plus any worsening attributable to natural progression, from the current level. You’re compensated for the increment, not the whole condition.
Practically: if you’re going to claim aggravation, find the older medical records that show what the condition looked like before. Without a baseline, there is nothing to measure against.
The Secondary Presumptives Nobody Cites
Two categories are written directly into the regulation as automatic, absent clear evidence to the contrary.
Cardiovascular disease after amputation. Ischemic heart disease or other cardiovascular disease in a veteran with a service-connected amputation of one leg at or above the knee, or both legs at or above the ankles, is held to be the proximate result of that amputation.
Conditions following traumatic brain injury. In a veteran with service-connected TBI, these are held to be the proximate result:
- Parkinsonism, including Parkinson’s disease, following moderate or severe TBI
- Unprovoked seizures following moderate or severe TBI
- Certain dementias — presenile dementia of the Alzheimer type, frontotemporal dementia, and dementia with Lewy bodies — if manifest within 15 years of moderate or severe TBI
- Depression if manifest within 3 years of moderate or severe TBI, or within 12 months of mild TBI
- Hormone deficiency diseases from hypothalamo-pituitary changes, if manifest within 12 months of moderate or severe TBI
Missing those time windows doesn’t end the claim. The regulation says explicitly that VA will still decide it under general service connection principles. The list in 38 CFR 3.310 is a shortcut, not a ceiling.
Common Secondary Chains
| Service-connected condition | Frequently claimed secondary | The mechanism |
|---|---|---|
| Knee or ankle injury | Opposite knee, hip, or lower back | Altered gait shifts load to the other side |
| Chronic pain from any orthopedic condition | Depression or anxiety | Persistent pain and lost function |
| PTSD | Sleep apnea, other sleep disturbance, hypertension, gastrointestinal conditions | Physiological effects of chronic stress |
| Diabetes | Peripheral neuropathy, retinopathy, kidney disease | Well-documented complications |
| Medication for a service-connected condition | Gastrointestinal damage, other side effects | Treatment effects, not the condition itself |
| Amputation | Cardiovascular disease | Written into the regulation as automatic |
That medication row is worth pausing on. Side effects of treatment for a service-connected condition are their own route, and veterans on long-term prescriptions rarely think to claim them.
The PTSD row rests on a genuine clinical relationship rather than a claims theory. The VA’s National Center for PTSD describes how PTSD disrupts sleep, which is the starting point for several of the chains veterans file.
What the Claim Needs
- A current diagnosis of the secondary condition.
- An established service-connected condition already rated.
- A medical opinion linking the two — the nexus. It should state the connection is “at least as likely as not,” and explain the reasoning rather than just asserting the conclusion.
- Baseline evidence, if you’re claiming aggravation rather than causation.
The nexus is where these claims are won and lost. An opinion that says “in my medical judgment, the altered gait documented since 2011 has placed abnormal load on the contralateral knee” is doing real work. One that says “his knee is related to his other knee” isn’t.
Where These Claims Get Denied
- No nexus opinion at all. The connection may be obvious to you and still needs a clinician to say it.
- A nexus with no reasoning. A one-line letter asserting a link, without explaining the mechanism, gets little weight.
- Claiming aggravation with no baseline records. There is nothing for VA to measure the increase against.
- The primary isn’t actually service-connected yet. Secondary claims depend on an existing award, so a pending primary claim has to be resolved first.
- Filing the secondary as a brand-new direct claim and having to prove an in-service event that never happened.
That last one is a paperwork problem more than a medical one. Say plainly on the claim which condition is primary and which is secondary, so the rater evaluates it under the right theory.
Why It’s Worth the Effort
Each additional rating raises your combined figure, and combined ratings behave in ways that reward filing. Our guide to how VA combines ratings and the bilateral factor covers that arithmetic.
Secondary ratings also feed the TDIU percentage thresholds — and because conditions from a common etiology or a single body system group together for that test, a secondary award can matter more than its own percentage suggests.
If your primary condition came through a presumptive route, our PACT Act guide covers what’s presumed, and lay evidence from family about the secondary condition’s daily impact belongs in the file — see how to write a buddy letter raters credit.
Frequently Asked Questions
What is secondary service connection?
Service connection for a condition caused by, or worsened by, a disability that is already service-connected.
Do I need to prove the condition started in service?
No. That’s the point of the secondary route — the service link is already established through the primary condition.
What is the difference between causation and aggravation?
Causation means the service-connected condition produced the new one. Aggravation means it made an existing nonservice-connected condition worse beyond its natural progression.
Why do aggravation claims need a baseline?
VA compensates only the increase. It deducts the baseline severity, plus natural progression, from the current level — so medical evidence of the earlier severity is required.
Is depression after a TBI automatically connected?
It is held to be the proximate result if it manifests within 3 years of a moderate or severe TBI, or within 12 months of a mild TBI, absent clear evidence to the contrary.
Can medication side effects be service-connected?
Yes. A condition caused by treatment for a service-connected disability can itself be service-connected as secondary.
Look at What You Already Have
The best first step costs nothing: pull your rating decision, list every service-connected condition, and ask what each one has done to the rest of your health since.
An accredited service officer will spot the chains you’ve stopped noticing. Our guide to free help from an accredited service officer explains how to reach one, or call Post 51 at (541) 451-1351.