How to Establish Secondary Service Connection for a VA Claim

Direct service connection ties a condition to something that happened while you served. Secondary service connection adds a second link: the condition came from a disability VA has already connected to service.

The rule is 38 CFR 3.310(a): "Disability which is proximately due to or the result of a service-connected disease or injury shall be service connected." The same paragraph adds that once granted, "the secondary condition shall be considered a part of the original condition."

"Proximately due to" is the key phrase. It means the service-connected condition is a real and direct cause, not a remote or possible one. VA's own examples on its when to file page are arthritis caused by a service-connected knee injury and heart disease caused by service-connected high blood pressure.

Three points that surprise people:

• The rating of the primary condition does not matter. The regulation requires a service-connected disease or injury. It does not require a compensable rating. A 0% condition can be the primary.
• Treatment counts as a cause. A condition caused by a medication or surgery prescribed for a service-connected disability is "the result of" that disability.
• The rule has one built-in presumption. Under 3.310(c), heart disease in a veteran with a service-connected amputation of a leg at or above the knee, or both legs at or above the ankles, is held to be the result of the amputation.

Veterans Benefits Administration (VBA) raters apply the rule using the M21-1 Adjudication Procedures Manual, which does not change the regulation but tells raters how to work through it.

Every secondary claim has the same 3 parts. VA needs evidence of each. Missing any one of them is the usual reason for a denial.

1. A current diagnosis of the secondary condition. A named condition in a treatment record, from VA or a private provider. Symptoms alone ("knee pain") are weaker than a diagnosis ("degenerative arthritis, left knee").
2. A service-connected primary condition. Your rating decision or the benefit summary letter from VA.gov lists your service-connected disabilities. The primary can also be claimed at the same time as the secondary, but the secondary cannot be granted until the primary is.
3. A medical nexus between the 2. A written opinion from a qualified clinician that the primary condition caused or aggravated the secondary one. VA's threshold is "at least as likely as not," which means a 50% or greater chance. The phrase tracks the reasonable-doubt rule in 38 CFR 3.102: when the evidence for and against is in "approximate balance," VA resolves the doubt in your favor.

The third element decides most cases. Under 38 CFR 3.159(a)(1), competent medical evidence comes from "a person qualified through education, training, or experience to offer medical diagnoses, statements, or opinions." Your own statement can describe symptoms and timing. It cannot supply the medical link. The medical nexus letters guide explains what a persuasive opinion contains.

Section 3.310 gives you 2 routes. They use different evidence and pay differently.

Causation, 3.310(a). The service-connected condition caused the new one. If VA agrees, it rates the secondary condition on its full severity. The knee-to-arthritis example is causation.

Aggravation, 3.310(b). You already had the condition for reasons unrelated to service, and a service-connected condition made it worse. The regulation says any increase in severity "proximately due to or the result of a service-connected disease or injury, and not due to the natural progress of the nonservice-connected disease, will be service connected." This route comes from the Court of Appeals for Veterans Claims in Allen v. Brown, 7 Vet. App. 439 (1995), which VA's Board of Veterans' Appeals still quotes in its decisions: additional disability from aggravation of a non-service-connected condition by a service-connected one "is also compensable."

Aggravation pays only for the added part. Under 3.310(b), the rater sets a baseline and a current severity under the rating schedule, then deducts the baseline and any natural progress. What remains is service-connected.

Watch out: The baseline rule. 3.310(b) says VA "will not concede" aggravation unless the baseline severity is "established by medical evidence created before the onset of aggravation," or by the earliest medical evidence between the onset and the evidence of current severity. If there is no record of how bad the condition was before it got worse, an aggravation claim has nothing to measure from. Old treatment records, even a single visit note, are the evidence that solves this.

VA lists the general evidence it needs on its evidence needed page: separation documents, service treatment records and medical evidence such as doctors' reports and test results. For a secondary claim, the evidence lines up with the 3 elements.

Source: https://www.ecfr.gov/current/title-38/chapter-I/part-3/subpart-A/subject-group-ECFR39a4b7a5c3a1d1c/section-3.310 and https://www.va.gov/disability/how-to-file-claim/evidence-needed/, effective September 2026.

Notes on each type:

• A Disability Benefits Questionnaire (DBQ). VBA publishes public DBQs your own provider can complete. VA does not pay for them. The Medical Opinion DBQ is not public, so the nexus goes in a separate letter.
• Private records. VA can request them if you sign VA Form 21-4142, Authorization to Disclose Information to VA. Sending them yourself is faster.
• Lay statements. Your own statement, or a witness statement on VA Form 21-10210, describes what you observe: when the new symptoms began, how they track the primary condition. Under 3.159(a)(2), lay evidence is competent for observable facts. It is not competent for the medical link. The medical evidence requirements guide covers how to get each type of record.

A secondary claim uses the same form as any other compensation claim. There is no separate "secondary" form.

1. Confirm the primary is service-connected. Check your rating decision or your benefit summary letter on VA.gov. If the primary is not yet granted, you can claim both at once; list the primary first.
2. Lock in your date. Submit an intent to file online, by phone or on VA Form 21-0966. It holds your effective date for 1 year while you gather evidence. Filing online sets the date the moment you start the form.
3. Get the diagnosis on paper. See a provider and make sure the secondary condition is named in the record.
4. Get the nexus opinion. Ask your treating clinician or an independent provider for a written opinion. For an aggravation claim, gather the earliest records of the condition for the baseline.
5. File on VA Form 21-526EZ. VA Form 21-526EZ, Application for Disability Compensation and Related Compensation Benefits, is the form. In the conditions section, name the secondary condition and state which service-connected condition it is "secondary to." Naming the primary tells the rater which route you are asking for. File online, by mail to the Claims Intake Center, PO Box 4444, Janesville, WI 53547-4444, in person at a regional office, or through a VA-accredited representative.
6. Attach the evidence. Upload the opinion, records and any DBQ with the claim. VA encourages sending everything you have so it can decide without extra development.
7. Attend the exam if VA schedules one. VA may order a VA claim exam (also called a C&P exam, for compensation and pension). Missing it without good cause can lead to a decision on the evidence already in the file. VA's how to file page shows its current average: 68.4 days for disability-related claims completed in August 2026. Claims that need an exam or opinion often take longer.

A VA-accredited representative can do steps 1 through 6 with you. A Veterans Service Organization (VSO) representative's help with a claim is always free. The filing your first claim guide covers the form itself.

Under 38 CFR 3.159(c)(4), VA must get an exam or a medical opinion when the file shows a current disability, a service-connected condition, and some indication the 2 may be linked, but does not have enough medical evidence to decide. For a secondary claim, VA usually asks its examiner 2 questions: caused by the service-connected condition, and if not, aggravated by it.

The examiner is a VA provider or a VA contract provider, and the exam is free. The examiner does not decide your rating or your claim; a rater does, using the exam alongside everything else in the file. You can ask for a copy of the exam report on VA Form 20-10206.

What VA weighs is the reasoning, on both sides. In a 2025 Board decision granting urinary dysfunction secondary to sleep apnea, the Board gave the VA examiner's negative opinion "no probative weight" because it "failed to support their conclusions with adequate rationale" and "did not specifically address the positive nexus opinion." The reasoned private opinion carried the claim.

Our C&P exam preparation guide explains what the DBQ measures.

A rated condition changes how you move, sleep or cope, or its treatment has effects of its own. The common patterns:

• Mechanical. A joint injury changes your gait and loads another joint or the spine. VA's knee-to-arthritis example is this type.
• Physiological. One disease process drives another. VA's high-blood-pressure-to-heart-disease example is this type.
• Mental health. Chronic pain or a mental health condition leads to a second diagnosis such as depression or a sleep disorder.
• Treatment side effects. A medication prescribed for the service-connected condition causes a diagnosed problem, such as reflux from long-term anti-inflammatory use. This is causation under 3.310(a). VA needs the prescription record, the diagnosis of the side effect, and an opinion tying them together.

The condition-by-condition lists, with the diagnostic codes and typical ratings for each pair, are in the common VA secondary conditions guide. This page stays on the process.

A granted secondary condition gets its own rating under the schedule. VA then combines it with your existing ratings under 38 CFR 4.25. Ratings are not added. VA lists them from most to least severe, combines them with Table I, then rounds to the nearest 10 (values ending in 5 round up). The regulation's own example: 50% and 30% combine to 65, which becomes 70%.

A new 10% rating may change nothing; a new 50% rating can move you 2 brackets. The VA math calculator runs any set of ratings, and the common secondary conditions guide has a worked example with the rates effective December 1, 2025. Some secondary conditions also carry Special Monthly Compensation (SMC) at level K, paid on top of the percentage; that guide covers it too.

The effective date for a secondary condition follows VA's general rule: the later of the date VA gets your claim or the date the condition began. That is why the intent to file in step 2 matters.

Does filing a secondary claim put my existing ratings at risk? A secondary claim asks VA to rate a new condition. It does not reopen your existing ratings, and long-held ratings carry their own protections. The understanding VA disability ratings guide sets out the 5-, 10- and 20-year rules and the proposed-reduction process.

Read the decision letter for the reason. Secondary denials nearly always name one of the 3 elements. The fix depends on which.

• No nexus, or the examiner said "less likely than not." The usual answer is a reasoned private opinion that addresses the examiner's reasoning. File it with a Supplemental Claim on VA Form 20-0995. New and relevant evidence reopens the claim and restarts VA's duty to assist, including a new exam if needed.
• No baseline for an aggravation claim. Find the earliest records of the condition and file them as new and relevant evidence, again on a Supplemental Claim.
• VA had the evidence and weighed it wrong. A Higher-Level Review on VA Form 20-0996 asks a senior reviewer to look for error. No new evidence is allowed, and you have 1 year from the decision.
• Primary not yet granted. Pursue the primary first, or together with the secondary on the same claim.

VA must explain why it found one opinion more persuasive than another; under 3.102, reasonable doubt "is not a means of reconciling actual conflict" in the evidence. The VA disability appeal guide walks through choosing a lane.

State benefits key off your combined percentage, not whether a rating is primary or secondary. A secondary grant that lifts you across a threshold such as 70%, 80% or 100% can open a property-tax exemption, a license plate, fee waivers or a dependent tuition benefit, depending on the state. Check the thresholds in the state veteran benefits finder.