Direct service connection is the most common way to establish that a disability is related to military service. It requires three elements, all of which must be satisfied: a current diagnosis, an in-service event or injury, and a medical nexus (link) between the two.
Element 1 — Current Diagnosis: You must have a current, diagnosed medical condition. The diagnosis must come from a qualified medical professional. A self-reported condition without a medical diagnosis is generally not sufficient, though some conditions (like tinnitus) are exceptions because they are subjective and self-reported by nature.
Element 2 — In-Service Event: There must be evidence of an event, injury, or illness during military service that is related to the claimed condition. This can be documented in service treatment records, service personnel records, buddy statements, or conceded based on the circumstances of service (for example, noise exposure for combat veterans). The event does not need to be a single dramatic incident — chronic exposure or the cumulative effect of service duties qualifies.
Element 3 — Medical Nexus: A medical opinion must link the current condition to the in-service event. The standard is "at least as likely as not" (50% or greater probability) that the condition is related to service. This opinion can come from a VA examiner during the C&P exam, a private physician, or a medical expert. A favorable nexus opinion from a private physician can be submitted with the claim and carries significant weight, especially if it explains the medical reasoning.
If any one element is missing, the claim will be denied. When you receive a denial, the decision letter tells you which element was not satisfied. Targeting new evidence at the missing element is the most effective strategy for a supplemental claim.
The "benefit of the doubt" doctrine (38 USC 5107(b)) requires that when the evidence is in approximate balance — roughly equal for and against — the VA must decide in the veteran's favor.
Note: This article references sections of the VA's M21-1 Adjudication Procedures Manual. The VA periodically reorganizes the M21-1 and section numbers may have changed since this article was written. For the most current section references, visit the VA's public M21-1 Web Automated Reference Material System (WARMS).