The three-legged stool
To win service connection for a VA disability claim, you need three things at once. VA lists them plainly on its evidence page for an original claim:
- "You have a current physical or mental disability"
- "You experienced an event, got injured, or became infected with a disease during your active-duty service"
- "There's a link between your current condition and the event, injury, or disease that happened during your service."
Think of these as three legs of a stool. Kick out any one leg and the whole thing falls. A diagnosis with no in-service cause is not service connected. An in-service injury that left no lasting condition is not a current disability. And a current condition plus an old injury still needs the link, called a nexus, to tie them together. This guide walks through each leg and the evidence that supports it.
Leg one: a current disability
The first leg is a condition you have now, physical or mental. A claim for a problem that has fully resolved, with nothing to rate today, does not clear this leg. This is where a current diagnosis and current treatment records matter.
VA lists medical evidence, described as doctor and hospital reports, among the records that support a claim. That evidence does not have to come only from VA. VA may consider private medical records, including a diagnosis, as evidence of a current condition, and it accepts records from private doctors and hospitals. A private diagnosis does not by itself establish service connection. If you have not been evaluated recently for the condition you are claiming, getting a current diagnosis on the record is a practical step. Browse the conditions library to see how VA frames specific diagnoses.
Leg two: an in-service event, injury, or exposure
The second leg is what happened during service. VA describes it as an event, an injury, or becoming infected with a disease during active-duty service. The evidence here usually lives in your service records.
VA specifically lists these among the documents that support a claim:
| Record type | What it shows |
|---|---|
| Discharge or separation papers (DD214 or equivalent) | Your service dates and character of service |
| Service Treatment Records, if in your possession | Injuries, complaints, and treatment during service |
| Medical evidence (doctor and hospital reports) | Diagnosis and treatment of the condition |
If the in-service event was witnessed but not written down, lay evidence can help. VA names lay evidence "like a buddy statement (VA Form 21-10210)" as a way to support a claim. A fellow service member who saw the injury or the exposure can describe what they observed firsthand.
Leg three: the nexus, or the link
The third leg is easy to overlook, and a missing link is what sinks a claim. You have to connect leg one to leg two. VA says it directly: "There's a link between your current condition and the event, injury, or disease that happened during your service."
How do you prove that link? VA tells you: "Usually we need medical records or medical opinions from health care providers to support this link. We may also accept lay evidence." A medical opinion that explains why your current condition is connected to your service is what is also called a nexus letter. It is a medical judgment, so it comes from a health care provider, not from a form you fill out yourself.
Some claims do not need you to prove this leg at all, because VA presumes the connection for certain conditions and exposures. See our presumptive conditions guide for how that works.
Matching each leg to the evidence you can gather
It helps to think in terms of what document proves what. Leg one is proved by current medical evidence, which VA describes as doctor and hospital reports. Leg two is proved by service records, and VA specifically names your DD214 or equivalent and your service treatment records if you have them. Leg three is proved by a medical opinion that supports the link, and VA adds that it may also accept lay evidence. When you line your evidence up this way, gaps become obvious: if you have a current diagnosis and service records but nothing that states the link, you have two legs and a wobble, not a finished claim.
Lay evidence deserves a note. VA names lay evidence "like a buddy statement (VA Form 21-10210)" as support for a claim. A buddy statement is a firsthand account, so it is strongest for describing events someone witnessed, such as an injury during training. It does not replace a medical opinion where medical judgment is what VA needs, but it can shore up the in-service event when the paperwork is thin.
Your job and VA's job
You are not left to gather everything alone, but you do have a duty. VA states it this way: "You must submit all relevant evidence in your possession and/or provide information sufficient to enable VA to obtain all relevant evidence not in your possession."
How much VA gathers depends on the claim path:
| Claim path | Who gathers what |
|---|---|
| Fully Developed Claim | VA "will only obtain service treatment records and Federal treatment records when you identify them" |
| Standard claim | VA "is responsible for getting relevant records from any Federal agency that you adequately identify and authorize VA to obtain" and will provide a medical exam or opinion if it decides one is needed |
On either path, you remain responsible for non-Federal records, although VA may assist and says it will make reasonable efforts on a standard claim when the records are adequately identified and authorized. That includes records from state or local governments, private doctors and hospitals, or current or former employers. If a private provider has records that support your claim, plan to get those yourself.
A hypothetical example
This is a made-up illustration, not a promise about any real case.
Marcus is a hypothetical veteran with knee pain today. Leg one is covered by a current diagnosis from his private orthopedist. Leg two is covered by a service treatment record showing he was treated for a knee injury during a training accident, plus a buddy statement from a squadmate who witnessed the fall. Leg three, the link, is covered by a medical opinion from his doctor explaining why the current arthritis is connected to that documented injury. All three legs are present, so the stool stands. Take away the medical opinion and VA is left with a current problem and an old injury but no stated link, which is exactly where a claim can stall.
What this does not mean
A diagnosis alone does not win a claim, and an in-service injury alone does not win a claim. You need all three legs at the same time: a current disability, the in-service event, and the link between them. Missing the link is the gap to watch for, because a current diagnosis and a service record can both be true while nothing on file explains how they connect.
The official VA pathway
Read VA's evidence pages, linked in the citations, to see exactly what supports each leg. You can file at VA.gov, and an accredited VSO can help you organize your records at no charge. If your condition may have been caused or worsened by another service-connected condition, look at secondary conditions too. VeteranHQ helps you understand the standard and organize your evidence. We do not prepare or file your VA claims.