A nexus letter is a written medical opinion from a licensed physician that establishes the legal connection between a condition you're claiming and your military service or a service-connected disability. Without it, the VA has no basis to grant a secondary claim.
The word "nexus" means link. That's exactly what the letter provides — the link the VA requires before it will assign a rating.
Why the Nexus Letter Is the Make-or-Break Document
The VA rates disabilities it finds service-connected. For secondary claims — where you're saying Condition B was caused by your already-rated Condition A — the nexus letter is how that medical relationship gets established on paper.
The VA examiner will produce their own opinion at your C&P exam. A well-written nexus letter from your own doctor counterbalances that opinion or prevents a negative one from being issued in the first place.
The Five Words Your Nexus Letter Must Contain
"At least as likely as not."
This phrase reflects the legal standard under 38 CFR § 3.102 and 38 CFR § 3.310. It means the probability that your service or primary condition caused or contributed to the claimed condition is 50% or higher.
Your nexus letter must use this exact phrase. A letter that says "consistent with," "may have been related to," or "could be secondary to" will fail. Those phrases don't meet the legal standard. The VA will deny on nexus and the letter will be useless.
What a Valid Nexus Letter Contains
A nexus letter that meets VA standards includes:
- Physician's credentials — name, license number, specialty, and contact information on letterhead
- The veteran's diagnosis — the specific secondary condition being claimed
- The primary condition — the service-connected disability the secondary is linked to
- The "at least as likely as not" standard — verbatim, no paraphrasing
- Medical rationale — the biological mechanism linking the two conditions (e.g., "PTSD-related hyperarousal disrupts sleep architecture and contributes to upper airway obstruction consistent with obstructive sleep apnea")
- Record review — a statement that the physician reviewed the veteran's records
Who Can Write a Nexus Letter
Any licensed physician (MD or DO) can write a nexus letter. There are three practical options:
Private Treating Physician
Your regular doctor. Pros: existing relationship, knows your history. Cons: many physicians are unfamiliar with VA standards and won't use the right language without guidance.
Solution: Bring our free nexus templates to your appointment and ask your doctor to review, modify, and sign the relevant one on their letterhead.
Independent Medical Expert (IME)
A physician hired specifically to provide a medical opinion for your VA claim. Pros: experienced with VA legal standards, produces the most defensible letters. Cons: costs $500–$2,500 typically.
VA Physician
A VA doctor can technically write a nexus letter, but most won't. The VA uses the C&P exam as its mechanism. Don't count on the VA to produce this for you.
What Gets a Nexus Letter Rejected
The VA will reject or discount a nexus letter for these reasons:
- Missing "at least as likely as not" language
- Vague rationale ("stress can cause many conditions")
- No record review stated
- Looks like a generic template with no personalization to the veteran's specific history
- One letter covering multiple conditions without individualized rationale for each
One letter per condition. Each one tailored to that specific medical relationship.
How to Get Your Doctor to Write One
Most veterans hand our free nexus templates to their doctor at a regular appointment and say: "I'm filing a VA secondary claim. Can you review this, fill in the relevant parts, and sign it on your letterhead?" Most physicians are willing when they understand what's being asked.
The templates provide the legal language. Your doctor isn't drafting from scratch — they're reviewing and signing a document that already meets the VA standard.