Some of the readjustment problems of Vietnam veterans have been attributed to posttraumatic stress disorder (PTSD). This case-control study compared demographic and military characteristics of 374 Vietnam veterans who had PTSD with 373 healthy Vietnam veterans. Veterans were chosen from the Agent Orange Registry, a Department of Veterans Affairs computerized database of approximately 200,000 Vietnam veterans who volunteered for a physical examination. Case patients and control subjects were frequently-matched by age, year of Registry examination, and race. Crude odds ratios (OR) were used to evaluate the risk of PTSD associated with certain characteristics of Vietnam service, as there was no apparent confounding by other military factors. Being wounded in Vietnam (OR, 2.33; 95% confidence interval (CI), 1.49-3.65) and having a combat job in Vietnam (OR, 1.54; 95% CI, 1.15-2.06) were the only risk factors for PTSD. Those who had noncombat jobs but were wounded had the highest risk of PTSD (OR, 3.56; 95% CI, 1.26-10.06).