The possibility that service in Vietnam has had an adverse effect on Vietnam veterans and is the cause of some of their current illnesses has been a controversial issue in the post-Vietnam period. Addressing this problem, a pathology study has been carried out at the Armed Forces Institute of Pathology (AFIP). Pathologic diagnoses found in Vietnam veterans have been compared with a control group of contemporary veterans without Vietnam service. This has revealed no statistically significant or unexplained differences in their demographic, anatomic, or morphologic findings. The essential similarity of their disease profiles to date fails to suggest the presence of any unique environmental factor that might have acted on the Vietnam group.