Most VA claims are denied not because the veteran doesn’t have a real service-connected condition — but because there’s no medical evidence clearly linking that condition to their service. The nexus letter is that link. It is a written opinion from a medical professional stating that your current condition is connected to your military service. Without it, many claims fail. With a strong one, many claims that were denied get approved on appeal.
What a nexus letter must say
The key phrase is: “at least as likely as not.” That is VA’s standard — a 50% or greater probability of connection. A nexus letter should state: (1) the physician reviewed your service records and medical history; (2) your current diagnosis; (3) their opinion that the condition is “at least as likely as not” caused or aggravated by your military service; and (4) a rationale explaining the medical reasoning. An opinion without a rationale is weak — VA can reject it. The rationale is what makes the letter compelling.
Who should write it
Your treating physician is the ideal author — they know your history and can speak to current diagnosis with authority. However, many treating physicians are reluctant to write nexus letters, either because they’re unfamiliar with VA standards or because their healthcare system discourages it. In those cases, independent medical experts who specialize in VA claims are an alternative. These are physicians who review your records and write a standalone nexus opinion — typically costing $300–$1,500 depending on complexity. For complex claims or high-value ratings, a strong independent nexus letter is often worth the investment.
Private nexus letters counter weak C&P exams
If a VA C&P examiner wrote an opinion that your condition is “less likely than not” service-connected, that negative opinion is in your file. To counter it, you need an equal or stronger positive opinion from a qualified medical professional. A well-reasoned private nexus letter that directly addresses the C&P examiner’s rationale and rebuts it is the standard strategy for overturning negative nexus opinions on appeal. “Dueling nexus letters” is common — VA is required to weigh the competing opinions, and the one with the better reasoning typically wins.
Using the nexus letter strategically
Submit the nexus letter with a Supplemental Claim if you already have a denial. Don’t submit it as a stand-alone document without connecting it to a specific claim action. Make sure the letter specifically references your service-connected condition by name and addresses the nexus to service — not just diagnosis. A letter that says “this veteran has knee pain” is not a nexus letter. A letter that says “this veteran’s knee pain is at least as likely as not the result of the ACL injury documented in their 2009 military medical records” is.