The 7 Paths to VA Service Connection

This guide explains the seven recognized ways a disability can be connected to military service. You will learn each path: direct service connection, presumptive service connection, secondary service connection, aggravation, and the other accepted routes the VA uses to grant service connection. For each one, you will find what evidence you need, how to gather it, and examples to help you spot which path fits your condition. Whether you are preparing your first claim or pursuing an appeal, this guide helps you understand your options and build a stronger service-connection case.

Notice: M21-1 Updated 2026-05-01

VA's adjudication manual (M21-1) was updated on May 1, 2026 to incorporate the holding in Spicer v. McDonough. The update revises guidance on aggravation of a non-service-connected disability by a service-connected disability (Path 4 / Path 5 below). The substance of this guide is being reviewed against the revised manual. Some specifics may change in a future update. Always verify with an accredited VSO or attorney before acting.

Quick Reference: All 7 Paths at a Glance

Scan this table to figure out which path fits your situation. Many claims use more than one.

Path What You Prove Key Law Nexus Needed?
1. Direct In-service event + current diagnosis + medical link between the two 38 USC § 1110 Yes
2. Presumptive Qualifying service + condition on VA's presumptive list 38 CFR § 3.309 No, the law presumes the link
3. TERA Toxic exposure + any condition plausibly linked 38 USC § 1168 VA must provide the exam
4. Secondary Service-connected condition caused or worsened a new disability 38 CFR § 3.310 Yes
5. Aggravation Pre-existing condition permanently worsened by military service 38 USC § 1153 Depends on the scenario
6. CUE A prior final VA decision was undeniably wrong 38 USC § 5109A No, based on old record
7. Section 1151 VA medical treatment caused a new disability 38 USC § 1151 Yes

Direct Service Connection

38 USC § 1110 (wartime) / § 1131 (peacetime) • 38 CFR § 3.303

This is the most common path. You prove that something happened in service, you have a current disability, and a medical professional links the two.

What You Must Prove (Shedden v. Principi, 2004)

  1. Current disability, a diagnosed medical condition right now, not just symptoms
  2. In-service event, an injury, illness, or exposure that occurred during active duty
  3. Nexus, a medical opinion stating it is "at least as likely as not" that your current disability is connected to the in-service event
Common mistake: Filing without a nexus opinion. An in-service event plus a current diagnosis is not enough by itself, the VA needs a medical opinion connecting the two. Without one, expect a denial.
The one exception: If your condition is a chronic disease listed under 38 CFR § 3.309(a), arthritis, hearing loss, hypertension, and about 40 others, you may not need a separate nexus opinion. Proving continuous symptoms since service can be enough on its own. See Walker v. Shinseki (2013). If your condition isn't on that list, get the nexus letter.

Presumptive Service Connection

38 USC § 1112 / § 1116 / § 1117 • 38 CFR §§ 3.307-3.309

If your condition is on the VA's presumptive list and you meet the service requirements, the VA presumes service connection, no nexus opinion needed. The law does the work for you.

What You Must Prove

  1. Qualifying service, 90+ days during a war period, or service at a specific location (Vietnam, Gulf, Camp Lejeune, etc.)
  2. Listed diagnosis, a condition on the applicable presumptive list under 38 CFR § 3.309
  3. Timely manifestation, typically within 1 year of discharge (some exceptions: MS is 7 years, certain cancers have no time limit)

Presumptive Categories

  • § 3.309(a), Chronic diseases: ~40 conditions including arthritis, diabetes, hypertension, hearing loss, tinnitus. Must reach 10% within 1 year of separation (3 years for TB / Hansen's, 7 years for MS, lifetime for ALS). Read the full list and windows.
  • § 3.309(c), POW diseases: Special conditions for former prisoners of war (base list for any POW, expanded list for 30+ days captivity). Read the POW presumption.
  • § 3.309(d), Radiation exposure: Cancers for veterans exposed to nuclear testing or Hiroshima/Nagasaki. Read the radiation list.
  • § 3.309(e), Agent Orange / Herbicides: Cancers and diseases for Vietnam, Thailand, and other exposure locations. Read the Agent Orange list.
  • § 3.309(f), Camp Lejeune: Water contamination from August 1953 through December 1987. Read the Camp Lejeune presumption.
  • PACT Act additions: 20+ new presumptives for burn pit and airborne hazard exposure. Read the burn-pit list.
Key case: Combee v. Brown (1994), even if you fail to meet presumptive criteria, you can still pursue direct service connection with actual evidence. The presumptive list is not the only way in.
Common mistake: Giving up when your condition is not on the presumptive list. That is where TERA (Path 3) comes in, keep reading.

TERA, Toxic Exposure Risk Activity

38 USC § 1168 • Created by the PACT Act (P.L. 117-168), Section 303 • Signed August 10, 2022

Presumptive vs. TERA, Two Lanes, Not One

Most veterans think there is one lane for toxic exposure claims: either your condition is on the presumptive list, or it isn't. That is wrong. The PACT Act created a second lane, and most people are driving right past it.

If you were denied because your condition is not on a presumptive list, you may still have a valid claim under 38 USC § 1168. This is a completely separate legal path that works even when the presumptive path does not.

What Is a Toxic Exposure Risk Activity?

Under § 1168(c), a TERA is any activity that requires an entry in the VA's exposure tracking system (like ILER, the Individual Longitudinal Exposure Record), or that the Secretary determines should qualify based on what is reasonably prudent to protect veterans' health.

TERA Exposure Categories

Air Pollutants

  • Burn pits
  • Sand, dust, particulates
  • Oil well fires
  • Sulfur fires (Mishraq)

Chemicals

  • Pesticides, herbicides
  • Depleted uranium
  • Contaminated water
  • Industrial solvents

Occupational Hazards

  • Asbestos
  • Lead-based paint
  • CARC paint
  • Firefighting foam (PFAS/AFFF)

Radiation & Warfare Agents

  • Nuclear weapons handling
  • Radioactive materials
  • Nerve agents
  • Chemical/biological weapons

How TERA Actually Works (Step by Step)

  1. You file a claim with evidence of (a) a current disability and (b) participation in a toxic exposure risk activity
  2. VA issues a TERA memorandum, a formal finding on whether you participated in a qualifying TERA
  3. If the finding is positive, VA concedes the toxic exposure occurred, you do not have to prove you were exposed
  4. VA provides a C&P exam at no cost, the statute requires it
  5. The examiner must consider the total exposure across all deployments and the synergistic, combined effect of all toxic exposures, not just one agent in isolation

Lane 1 vs. Lane 2: Side-by-Side

Feature Lane 1: Presumptive Lane 2: TERA (§ 1168)
Condition must be on a VA list? Yes, 38 CFR § 3.309 No, any condition with a plausible toxic exposure link
Nexus opinion needed? No, the law presumes the connection Yes, but VA must provide the exam free
What is conceded? The entire connection (exposure + causation) The toxic exposure occurred, causation still needs an opinion
Works for rare/unlisted conditions? No, only listed conditions qualify Yes, this is the primary advantage
Combined exposure analysis required? No Yes, all exposures across all deployments
Who bears the burden of getting a nexus opinion? Nobody, presumption eliminates the need VA, the statute requires VA to provide the exam
Key statute 38 USC §§ 1112, 1116, 1119 38 USC § 1168

What TERA Gets You That Presumptive Doesn't

  • Coverage for conditions not on any list. Rare cancers, autoimmune conditions, neurological disorders, if there is a plausible link to toxic exposure, TERA forces VA to evaluate it.
  • A free C&P exam and nexus opinion. Under direct service connection, if VA declines to order an exam, you may have to pay for a private nexus letter ($1,500-$5,000). Under TERA, the exam is mandatory.
  • Combined/synergistic exposure analysis. The examiner must consider ALL exposures together, burn pits + depleted uranium + contaminated water, not each in isolation.
  • A lower initial barrier. You need evidence of a disability plus evidence of TERA participation. You do not need to independently prove the nexus before filing.

Qualifying Locations (Burn Pit / Airborne Hazard Concession)

  • Southwest Asia theater (August 2, 1990-present): Iraq, Kuwait, Saudi Arabia, Bahrain, Qatar, UAE, Oman, Somalia, plus associated waterways
  • Post-9/11 (September 11, 2001-present): Afghanistan, Djibouti, Egypt, Jordan, Lebanon, Syria, Uzbekistan, Yemen

When TERA Does Not Apply

Under § 1168(b), VA is not required to provide a TERA exam when:

  • The disability is based on physical trauma (a broken bone from an accident)
  • The disability is a mental disorder (unless the mental disorder is related to toxic exposure)
  • There is no indication of any association between the disability and the TERA
The claim most veterans miss: If your VSO filed your toxic exposure claim as presumptive-only and it got denied because your condition isn't on the list, you may have a TERA claim sitting right there. Ask about 38 USC § 1168. A supplemental claim citing TERA could change the outcome.
How to reference TERA in your claim: When filing, specifically state that you are claiming service connection under 38 USC § 1168 and request a TERA memorandum. List every toxic exposure from every deployment. The more specific, the better.

Secondary Service Connection

38 CFR § 3.310

If a condition you already have service connection for caused or worsened a new condition, that new condition can be service-connected too. This is one of the most underused paths.

What You Must Prove

  1. An existing service-connected disability (the "primary" condition)
  2. A new, current disability (the "secondary" condition)
  3. A medical link showing the secondary was either caused by or aggravated by the primary

The Two Theories

  • Causation: The service-connected condition directly caused the new one (e.g., diabetes causing peripheral neuropathy)
  • Aggravation: The service-connected condition made a pre-existing non-service-connected condition permanently worse (established by Allen v. Brown, 1995). Compensation is for the degree of worsening above the baseline.
Common secondary claims: PTSD causing sleep apnea • Knee injuries causing hip/back problems • Diabetes causing neuropathy, ED, or kidney disease • Medications causing side effects (ED, weight gain, GI problems)
Common mistake: Only filing under the causation theory. If causation fails, the aggravation theory under Allen is a separate argument, make sure your nexus letter addresses both.

Aggravation of a Pre-Existing Condition

38 USC § 1153 • 38 CFR § 3.306 • Presumption of soundness: 38 USC § 1111

If you had a condition before service that got permanently worse during service, this path applies. The rules depend on whether the condition was noted at your entrance exam.

Scenario A: Condition NOT Noted at Entry

You are presumed healthy at entry under 38 USC § 1111. To deny your claim, the VA must prove both of the following with clear and unmistakable evidence (the highest standard in VA law):

  1. The condition pre-existed service, AND
  2. The condition was not aggravated by service

If VA fails on either prong, you win, and it is treated as direct service connection, not aggravation. This is the Wagner v. Principi (2004) standard.

Scenario B: Condition Noted at Entry

You must show an increase in disability during service. Once you do, the presumption of aggravation kicks in. VA can only rebut it by showing the increase was due to the natural progression of the disease.

Common mistake: VA improperly placing the burden on the veteran. Under Wagner, when a condition is not noted at entry, the burden is entirely on VA, and the standard is "clear and unmistakable." If a VA decision puts the burden on you to prove aggravation when nothing was noted at entry, that decision may be wrong.
Flare-up vs. aggravation: A temporary worsening that resolves is a flare-up, not aggravation. To qualify, the worsening must be permanent and beyond the natural course of the condition.

Clear & Unmistakable Error (CUE)

38 USC § 5109A (Regional Office decisions) / § 7111 (Board decisions) • 38 CFR § 3.105(a)

CUE is not a new claim, it is a motion to fix a past VA decision that was undeniably wrong. If you win, the effective date reverts to the original decision, potentially decades of back pay.

What You Must Prove (Russell v. Principi, 1992)

  1. The correct facts were not before the adjudicator, or the law was incorrectly applied
  2. The error is undebatable, not a judgment call or a weighing-of-evidence disagreement
  3. The error would have manifestly changed the outcome
No time limit. A CUE motion can be filed at any time, there is no deadline. And the potential payoff (retroactive compensation to the original decision date) can be enormous.
Common mistake: Treating CUE like an appeal. You cannot submit new evidence. You cannot re-argue how evidence should have been weighed. The error must be based on the record and law as they existed at the time. Per Fugo v. Brown (1993), vague allegations fail, you must identify the specific error and explain how the outcome would have been different. Consider hiring an accredited attorney for CUE motions.

38 USC § 1151, VA Treatment Injuries

38 USC § 1151 • 38 CFR § 3.361

If VA medical treatment, surgery, or a VA exam caused a new disability or made an existing one worse, you may be compensated as if it were service-connected, even though it has nothing to do with your military service.

What You Must Prove

  1. Additional disability, a new condition or worsening that was not present before the VA treatment
  2. Caused by VA care, hospital care, medical/surgical treatment, an exam, or vocational rehab
  3. Proximate cause, one of two theories:
    • Fault: Carelessness, negligence, lack of proper skill, error in judgment, or failure to obtain informed consent
    • Unforeseeable event: A complication that a reasonable provider would not have considered an ordinary risk
Informed consent matters. Even if the VA provider was not negligent, if they failed to adequately explain the risks of a procedure and you suffered a known complication, the informed consent failure can win the claim. Check whether the consent form in your records properly documented the risks (per 38 CFR § 17.32).
Also file a Federal Tort Claims Act (FTCA) claim. Section 1151 and FTCA are not mutually exclusive. 1151 gets you monthly compensation; FTCA can get a lump-sum damages award. The FTCA has a 2-year statute of limitations, do not wait.

Strategy: Using Multiple Paths at Once

The 7 paths are not mutually exclusive. VA must consider all applicable theories of entitlement when you file a claim (Schroeder v. West, 2000). Smart claims use multiple paths simultaneously.

Example: Veteran With Lung Disease After Burn Pit Exposure

  • Path 2 (Presumptive), if the lung condition is on the PACT Act presumptive list
  • Path 3 (TERA), if it's NOT on the list, force VA to evaluate the toxic exposure link
  • Path 1 (Direct), with an independent nexus opinion linking burn pit exposure to the condition
  • Path 4 (Secondary), if the lung disease was caused by medication for a different service-connected condition

Filing under multiple paths costs nothing extra and gives you multiple chances to win.

Effective Date Implications

  • Presumptive, TERA, direct, secondary, and aggravation claims typically use the date of claim filing (or Intent to File) as the effective date
  • CUE can go back to the date of the original erroneous decision, potentially decades of back pay
  • Section 1151 typically uses the date of claim or date the injury occurred
  • Understanding which path yields the best effective date is part of the strategy, see our Effective Dates guide
Bottom line: If you have toxic exposure and your condition is not on a presumptive list, do not stop there. File under TERA (38 USC § 1168). If you have an old denied claim that was wrongly decided, consider CUE. If VA treatment hurt you, file 1151. Know all 7 paths, use every one that applies.

This guide is for educational purposes only and is not legal or medical advice. All legal references are from Title 38 of the U.S. Code and the Code of Federal Regulations. Case citations are provided for informational purposes. For help with your specific claim, find a free VSO representative or consult with a VA-accredited attorney.