The evidence a rater weighs most

VA Nexus Letters: What They Must Say

A nexus letter is the medical opinion connecting your condition to your service — stated to the VA’s “at least as likely as not” standard, reasoned from your records, and signed by a licensed clinician. Below: what yours must contain, condition by condition, and a complete real example you can read before writing a word.

Read the example letter — free Draft yours from your records

The example: 4,348 words · 11 verified studies · published in full, no account.

Sample — Illustrative Specimen

Invented veteran · fictional sample provider · not a signed medical opinion

INDEPENDENT MEDICAL OPINION

Veteran: Samuel Okonkwo (invented veteran — illustrative sample)
Condition at issue: Obstructive Sleep Apnea (ICD-10 G47.33)
Service-connected condition relied upon: Chronic Sinusitis (ICD-10 J32.9)
Basis of claim: Secondary service connection under 38 C.F.R. §§ 3.303, 3.310
Opinion date: August 4, 2026

REASON FOR EVALUATION

This is an independent medical opinion prepared for the purpose of assisting in the determination of eligibility for veterans benefits. Its single question is a medical one: whether Mr. Okonkwo's obstructive sleep apnea is proximately due to, the result of, or aggravated beyond its natural progression by his service-connected chronic sinusitis. It is addressed to the C&P examiner and the VA rating official who will weigh it.

MEDICAL OPINION

It is my opinion that it is at least as likely as not (a 50 percent or greater probability) that Obstructive Sleep Apnea is proximately due to, the result of, or aggravated beyond its natural progression by the veteran's service-connected Chronic sinusitis (38 C.F.R. §§ 3.303, 3.310). In short: but for the veteran's service-connected Chronic sinusitis, Obstructive Sleep Apnea would not have occurred, or would not have progressed to its current severity.

Based on the history and records reviewed and the medical literature governing this condition, I opine that Obstructive Sleep Apnea (ICD-10 G47.33) is proximately due to, the result of, or aggravated by his service-connected Chronic sinusitis (ICD-10 J32.9), under 38 C.F.R. § 3.310. This claim is brought as secondary to Chronic sinusitis, established as service-connected in the veteran's VA claims file; the opinion below rests on that anchor. The mechanism connecting the two conditions — chronic nasal and sinonasal obstruction increasing upper-airway resistance and collapsibility during sleep — is well established in the peer-reviewed literature and applies directly to a claimant, like Mr. Okonkwo, whose sinonasal disease began in service and whose obstructive sleep apnea was later confirmed on polysomnography. My opinion accounts for the recognized non-service risk factors for this condition, none of which displaces the sinonasal pathway as at least an equal and materially contributing cause.

Read all 4,348 words — free

The published example letter — an invented veteran and a fictional sample provider.

The short answer

Do I need a nexus letter, and who can write one?

You need a nexus letter when nothing else in your file connects your diagnosis to your service: most conditions diagnosed after you got out, and most secondary claims. You usually don't for a presumptive condition, and may not when a chronic condition was diagnosed in service and treated continuously since. Any qualified medical professional can write one, VA or private, and it has to be their own reasoned opinion, signed by them.

Ask your own doctor with a one-page request →Commander Health (physical conditions) →Can AI write a nexus letter? →

What is a nexus letter?

A nexus letter is a written medical opinion from a licensed clinician stating that a veteran’s condition is “at least as likely as not” — a 50 percent or greater probability — connected to their military service, or to a condition the VA has already service-connected. “Nexus” is simply the legal word for that connection. The letter’s job is to give the rater medical reasoning they can weigh: the diagnosis, the theory of connection, and a rationale grounded in the records and the medical literature.

The standard · 38 CFR § 3.102

“At least as likely as not”

The opinion does not have to be certain, or even “more likely than not.” A 50 percent or greater probability meets the standard; when the evidence is in approximate balance, the benefit of the doubt goes to the veteran.

Before you ask a doctor

Does your claim need one?

Every service-connection claim has to show three things: a current diagnosis, an in-service event, and a link between them. The nexus letter carries the third — so whether you need one depends on whether something else already carries it.

The clearest signal

A denial that says “the evidence does not show a link between your current condition and your military service” is the VA telling you the nexus element is missing.

Usually not
Presumptive conditions
For conditions the law presumes are service-connected — Agent Orange, PACT Act toxic exposures, Gulf War presumptives — qualifying service plus a current diagnosis carries the link by statute.
Sometimes
Chronic conditions documented in service
When a chronic condition was diagnosed in service and treated continuously since, the records themselves may carry the link.
Usually yes
Everything else — and nearly every secondary claim
Conditions diagnosed years after separation, and secondary claims, where the link between two conditions is a medical question only a medical opinion can answer.

38 C.F.R. § 3.102 · the benefit of the doubt

The words that meet the standard

The VA does not require certainty. Under its benefit-of-the-doubt rule, when the evidence for and against a claim is in approximate balance, the tie goes to the veteran. So an opinion only has to reach “at least as likely as not” — a 50 percent or greater probability. Fifty-fifty is enough.

“It is my opinion that the veteran’s [condition] is at least as likely as not (50 percent or greater probability) related to [the in-service event, or the service-connected condition].”

Meets it

“At least as likely as not”
“More likely than not”
“Is related to” / “was caused by”

Falls short

“May be related”
“Could be connected”
“Is possibly related”

Speculative language like “may” has repeatedly been held too weak to establish a link. A doctor who supports your claim but writes “may be related” out of caution is writing a letter the VA can discount — often it helps just to show them that the question is 50 percent or greater, not certainty.

Who signs it

Who can write one?

Any licensed clinician qualified to diagnose and opine on your condition. It does not have to be a VA doctor or an outside “independent” examiner.

A physician — MD or DO
A nurse practitioner (NP) or physician assistant (PA)
A psychologist (PhD or PsyD), for mental health conditions
A specialist for the condition — orthopedist, audiologist, neurologist
Your own treating provider, who already knows your history

Specialty matters to weight — a cardiologist on a heart condition carries more than an unrelated specialist. And the opinion must be the clinician’s own: a draft can save them time, but they review the records, use their own judgment, and sign only what they actually believe.

Caluza v. Brown, 7 Vet. App. 498 (1995)

The three elements

Service connection rests on three elements. A strong letter speaks to all three — and the third is its whole job.

An in-service event, injury, or diseaseSomething that happened in service — an injury, an exposure, an illness, or a stressor.
A current diagnosisA present-day condition a clinician has identified — not symptoms alone.
A nexusThe medical link between the two: the reasoned opinion that the in-service event caused or contributed to the diagnosis.

What a rater weighs

Strong letter vs. weak letter

Two letters can reach the same conclusion and carry very different weight. The difference is almost always the rationale — an opinion that states a conclusion without explaining the medicine can be given little or no weight, even with the right words.

What separates a strong nexus letter from a weak one
Element	Strong letter	Weak letter
Records review	Names the records reviewed, with dates	No sign the provider saw the file
Probability language	“At least as likely as not (50% or greater)”	“May be related,” “possibly connected”
Rationale	Explains the medical mechanism from cause to condition	Asserts the conclusion without saying why
Specificity	This veteran’s history, findings, and timeline	Generic language that could fit anyone
Literature	Cites supporting medical literature where it exists	Nothing beyond the assertion
Credentials	Specialty and license stated; signed and dated	Unsigned, undated, or credentials missing

Check a nexus letter you paid forWhat to look for before you file it.Open Why template letters get flaggedAnd what a rater weighs instead.Open Ask your own doctorA one-page request with the checklist the VA looks for.Open

44 condition guides

What yours must say — by condition

Each guide covers the diagnostic code, the connection theories that fit the condition, the secondary pathways veterans actually file, and why letters for it get discounted.

38 C.F.R. § 3.310

For secondary claims

A secondary nexus letter answers a different question: whether the claimed condition was caused — or made worse — by a condition the VA already service-connected. It connects the new condition to that anchor, not all the way back to service.

Spicer v. McDonough, 61 F.4th 1360 (Fed. Cir. 2023), held that this is a “but-for” question — broader than the stricter proximate-cause test the VA had sometimes applied. The strongest opinions explain the mechanism and reason through it: would the condition, or its worsening, have happened without the service-connected one?

Secondary service connection, explained →Spicer and the M21-1 update →

How VA Claim Commander helps

A starting point, not a blank page

Intake gathers your diagnosis, treatment history, and the in-service event in plain language.
It reads your records and pulls out the diagnoses, dates, and providers that matter.
It drafts a letter that speaks to all three elements and states the standard correctly.
Your clinician gets a clear starting point to review against your records.

The draft is never a finished or signed medical opinion. A licensed clinician must independently review your records, revise the draft to their own judgment, and sign only an opinion they actually hold. If the medicine doesn’t support a connection, no document should claim one.

Common questions

Do I need a nexus letter?

You need one when nothing else in your file links your current diagnosis to your service or to a service-connected condition: most conditions first diagnosed years after separation, and nearly every secondary claim. You usually don't for a presumptive condition, where qualifying service plus a diagnosis carries the link by law. You may not when a chronic condition was diagnosed in service and treated continuously since, because the records can carry the link.

Can my VA doctor write a nexus letter?

They can, but they don't have to. A VA treating provider may write a medical statement for you, and like any opinion it is weighed on its reasoning. No clinician has to give an opinion they don't hold, and some VA providers decline. Asking with a short summary of your records and the exact question makes it easier to say yes.

How much does a nexus letter cost?

It varies. A treating provider may write one as part of your care or charge for the time to review records, and private opinion services charge more. Ask the full price before you agree, and be wary of anyone selling a letter without reviewing your records, or promising a result.

Can VA Claim Commander write my nexus letter?

No one but a clinician can give the opinion. VA Claim Commander reads your records and drafts a letter for a clinician to review, revise, and sign only if they agree. Through Commander Health, a licensed clinician reviews your records for a physical condition for $500 and can decline if the records don't support an opinion; it does not provide opinions for PTSD or other mental health conditions. For those, ask your treating mental health provider.

What is a nexus letter?

A nexus letter is a written medical opinion from a licensed clinician stating that a veteran's condition is "at least as likely as not" (a 50 percent or greater probability) connected to their military service, or to a condition already service-connected. It bridges the diagnosis and the service connection with medical reasoning a VA rater can weigh.

Who can write a nexus letter?

Any licensed medical professional opining within their specialty — a physician carries the most weight for most conditions. The clinician must review the records, exercise independent judgment, and sign with their credentials. VA Claim Commander drafts the letter from your own records and story; your clinician reviews and signs it.

Does the VA require a nexus letter?

Not formally — but when service connection isn't presumptive or already established, the nexus opinion is usually the deciding evidence. C&P examiners write their own opinion either way; a strong private nexus letter puts a well-reasoned counterweight in the file before they do.

What makes a nexus letter strong?

Four things raters weigh: the exact "at least as likely as not" standard, a named theory of connection (38 C.F.R. § 3.303 direct or § 3.310 secondary), a rationale grounded in the records and the medical literature rather than a bare conclusion, and credentials from a clinician whose specialty covers the condition.

See the standard before you write a word

Read the complete example letter free, then draft yours from your own records — for a licensed clinician to review and sign.

Read the example letter Draft yours from your records

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