A nexus letter is the most critical piece of evidence in a VA disability claim. Learn what makes a nexus letter strong, who should write it, common mistakes, and how the BVA evaluates nexus opinions.
A nexus letter is a medical opinion that links ('connects') a veteran's current disability to their military service. It is the single most important piece of evidence in most VA disability claims — and the most common reason claims are denied is an inadequate or missing nexus opinion. The BVA requires that nexus opinions use the 'at least as likely as not' standard (50% or greater probability), provide a clear rationale explaining the medical mechanism, and be written by a qualified medical professional who reviewed the veteran's service and medical records. The most common nexus letter mistakes include: using conclusory language without explaining the reasoning ('it is my opinion that...' without the 'because'), failing to address contrary evidence in the record, not specifying whether the opinion covers direct causation, secondary connection, or aggravation, and using a provider who lacks relevant specialty credentials. A strong nexus letter from a board-certified specialist in the relevant field, based on a thorough record review and in-person examination, carries significantly more probative weight at the BVA than a generic letter from a primary care provider. Veterans should also know that the BVA can — and frequently does — reject VA C&P exam opinions that are inadequate, ordering remands for new examinations. If your C&P exam was cursory or the examiner didn't review your records, that negative opinion can be challenged.