What is a nexus letter?

Key Takeaways

A nexus letter is a written medical opinion from a qualified healthcare provider that connects a veteran’s current condition to their military service. It is often the single most important document in a VA disability claim, and a poorly drafted one is one of the most common reasons the VA denies claims. Working with a veterans disability attorney before obtaining a nexus letter can help ensure the opinion meets the VA’s legal standard and holds up through review.  

Every VA disability claim rests on three pillars: a current diagnosis, an in-service event or injury, and a documented link between the two. The first two pillars are often straightforward. The third — the medical nexus — is where claims are won and lost. Whether a claim involves PTSD, a physical disability, or traumatic brain injury, the nexus letter is often the piece that determines whether the VA grants or denies service connection. 

At the Law Office of Sean Kendall, our experienced team of attorneys helps veterans nationwide navigate the VA disability claims process. You fought for us — let us help you fight for the benefits you deserve. Here's what you should know about nexus letters and how we can assist you.

What Is a Nexus Letter? 

A nexus letter — sometimes called an Independent Medical Opinion (IMO) — is a written statement from a licensed medical professional that provides a professional opinion about the relationship between a veteran's diagnosed condition and their military service. The letter must state, at a minimum, that the condition is "at least as likely as not" caused or aggravated by in-service events.

That phrase — "at least as likely as not" — reflects the VA's benefit-of-the-doubt standard. The VA is required to resolve reasonable doubt in the veteran's favor. A nexus letter that meets this threshold shifts the burden and gives the VA the foundation it needs to approve the claim. 

What Makes a Nexus Letter Strong? 

Not all nexus letters carry equal weight. The role of experts in writing an effective nexus letter is to provide a credible, well-reasoned opinion that the VA cannot easily dismiss. The key elements of a strong letter include: 

• Credentials of the author. The letter should be written by a licensed physician, ideally a specialist in the relevant field. VA physicians cannot write nexus letters because they are not independent. 

• Review of the records. A strong nexus letter is based on a review of the veteran's service records, medical history, and relevant research — not just a brief clinical note. 

• The correct legal language. The letter must state that the condition is "at least as likely as not" related to service. Weaker language — "possibly," "could be," or "may be" — often does not meet the threshold. 

• Medical rationale. The opinion should explain the reasoning behind the conclusion, citing the veteran's specific service history, known risk factors, and any relevant medical literature. 

• Acknowledgment of alternative causes. A nexus letter that addresses and refutes potential alternative explanations is more persuasive than one that ignores them. 

When Is a Nexus Letter Required? 

The VA requires a nexus letter whenever service connection is not already presumptive. For presumptive service connections, the VA accepts that certain conditions are related to specific types of service without requiring individual proof. For all other claims, the veteran must affirmatively demonstrate the connection, and a nexus letter is the means of doing so. Nexus letters are particularly important in: 

• Secondary service connection claims, where one diagnosed condition is claimed to have caused or aggravated a second condition 

• Claims involving delayed-onset conditions, such as asbestos-related lung disease or PTSD symptoms that appeared years after discharge 

• Claims where the VA's own examiner has provided a negative or inconclusive nexus opinion 

• Appeals where service connection was denied, and the veteran is presenting new evidence 

How Does an Attorney Help With the Nexus Letter Process? 

Veterans are entitled to obtain a private nexus letter at any stage of the claims process. However, drafting an effective medical opinion is more than just finding a willing doctor. A veterans disability attorney can help by: 

• Identifying the appropriate specialist for the specific condition at issue 

• Gathering and organizing the service records, military occupational specialty documentation, and medical history the expert will need to review 

• Briefing the expert on the applicable legal standard so the letter uses the correct language 

• Reviewing the draft letter before submission to confirm it meets VA requirements 

• Challenging VA nexus opinions that are inadequate, incomplete, or based on an insufficient examination 

This is especially important when a Compensation and Pension (C&P) examiner provided a negative opinion. Overcoming an adverse C&P opinion requires a competing independent medical opinion that is at least as well-reasoned. Our firm has extensive experience working with medical experts to build effective nexus opinions across a wide range of claim types. 

What Types of Claims Benefit Most From Attorney-Guided Nexus Letters? 

Nexus letters are particularly beneficial in the following types of VA disability claims:

• TBI and cognitive impairment claims, where the nexus must link a specific in-service event to current neurological symptoms 

• Secondary condition claims, where the causal chain runs through multiple diagnoses 

• Toxic exposure claims for conditions not yet listed as presumptive 

• Claims involving complex occupational histories, such as Navy veterans with asbestos exposure or Gulf War veterans with multiple undiagnosed conditions 

Veterans pursuing TDIU benefits often need nexus letters not only to establish service connection but also to document how the combined effect of service-connected conditions prevents substantially gainful employment. When that case is well-built, the nexus letter becomes the cornerstone of a successful claim.