OBJECTIVE Although studies have suggested a disproportionate rate of suicide among war veterans, particularly those with postservice psychiatric illness, there has been little systematic examination of the underlying reasons. This study aimed to identify factors predictive of suicide among Vietnam combat veterans with posttraumatic stress disorder (PTSD). METHODS Of 187 veterans referred to the study through a Veterans Administration hospital, 100 were confirmed by means of a structured questionnaire and five clinical interviews as having had combat experience in Vietnam and as meeting the DSM-III criteria for PTSD. The analysis is based on these 100 cases. RESULTS Nineteen of the 100 veterans had made a postservice suicide attempt, and 15 more had been preoccupied with suicide since the war. Five factors were significantly related to suicide attempts: guilt about combat actions, survivor guilt, depression, anxiety, and severe PTSD. Logistic regression analysis showed that combat guilt was the most significant predictor of both suicide attempts and preoccupation with suicide. For a significant percentage of the suicidal veterans, such disturbing combat behavior as the killing of women and children took place while they were feeling emotionally out of control because of fear or rage. CONCLUSIONS In this study, PTSD among Vietnam combat veterans emerged as a psychiatric disorder with considerable risk for suicide, and intensive combat-related guilt was found to be the most significant explanatory factor. These findings point to the need for greater clinical attention to the role of guilt in the evaluation and treatment of suicidal veterans with PTSD.