A nexus letter for a secondary condition is a medical opinion that a new condition was caused or made worse by a disability VA has already service-connected. It does not have to connect to your time in service. It connects to your existing rating. The provider’s job is to explain why, in medical terms, and to state the opinion at the “at least as likely as not” level.
What is secondary service connection?
Under 38 CFR 3.310, a disability caused by a service-connected disease or injury is itself service-connected. The same rule covers aggravation: if a service-connected condition worsens another condition beyond its natural progression, VA can service-connect the worsening. VA measures aggravation against a baseline severity, so earlier medical records matter.
Common pathways include chronic pain leading to depression or anxiety, PTSD leading to sleep problems, a knee condition changing your gait and straining your hip or back, and side effects from medicine you take for a service-connected condition. Our guide to secondary service connection covers the concept in full.
How is a secondary nexus letter different from a primary one?
A primary letter asks whether a condition is linked to service. A secondary letter asks whether it was caused or aggravated by a specific service-connected condition. The standard is the same, at least as likely as not (a 50% or greater probability). The reasoning changes: instead of reviewing service records for an event, the provider looks at the medical relationship between the two conditions and your own history.
What should a secondary nexus letter include?
- The service-connected condition. Name it and, if you know it, the current rating.
- The new diagnosis. Stated in clear medical terms.
- A review of your records. The letter should say what the provider reviewed.
- The reasoning. The core of the letter: how the first condition causes or aggravates the second, tied to your history and to accepted medical understanding. Generic statements are weaker than reasons that refer to your case.
- A clear opinion. For example: “It is my medical opinion that the veteran’s [condition] is at least as likely as not caused or aggravated by the service-connected [condition].”
- Provider credentials and signature.
For a wider look at wording and what to avoid, see our guides to what a nexus letter is and the nexus letter template.
Which provider should write it?
Any licensed provider can write a nexus letter, including your own treating doctor, and VA does not require a paid one. Choose someone who understands the condition in question, for example a psychiatrist for mental health, a sleep specialist for sleep apnea or an orthopedist for joint problems. If your doctor is willing but unsure of the format, you can share your records, a timeline and a plain-language list of what the letter should cover.
If your doctor declines, Woobie offers independent medical opinions written by licensed medical professionals for a flat fee that is never tied to the outcome. VA decides what weight any opinion gets, and results vary. We do not file claims. For filing help, accredited VSO representatives are free; find one on VA.gov.
Examples of secondary pathways with their own guides
Frequently asked questions
Can any condition be claimed as secondary?
A condition can be claimed as secondary if a service-connected condition caused it or made it worse. The claim needs a medical opinion supporting that link at the at-least-as-likely-as-not level. VA decides whether the evidence is enough, and results vary.
Does the secondary condition have to start after the service-connected one?
Not always. Under VA’s aggravation rule, a condition you already had can qualify if a service-connected condition worsened it beyond its natural progression. VA compares the current severity with a baseline, so earlier medical records help.
Can I have more than one secondary condition from the same service-connected condition?
Yes. One service-connected condition can lead to more than one secondary claim if the medical evidence supports each link. Each secondary condition needs its own supported opinion.
What if my doctor has never written a nexus letter?
You can share your records, a timeline and a short list of what the letter should cover. An accredited VSO can explain what VA looks for at no cost. If your doctor still declines, you can ask a different provider or an independent medical opinion provider.
Questions about your medical evidence? Woobie offers a free consultation to talk through your situation. Woobie is not a law firm or an accredited claims agent and does not file claims. Schedule a free consultation →