The authors examined the effects of wartime stressors in a sample of 69 Vietnam veterans who were psychiatric inpatients in a Veterans Administration hospital. Participation in atrocities and the cumulative exposure to combat stressors, each independently of the other, conferred a significant risk for posttraumatic stress disorder. In contrast, the effect of these war experiences on the onset of panic, major depression, and mania was not significant. The results indicate that extreme stressors are uniquely linked with posttraumatic stress disorder's characteristic cluster of symptoms but challenge DSM-III's implicit assumption that the reexperienced trauma is the stressor responsible for posttraumatic stress disorder.