Assessment data from 118 Vietnam-era veterans seeking psychological services at two Los Angeles Veterans Administration Medical Centers were analyzed to examine the potential relationships between number of preadult and adult antisocial behaviors, as defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-III; American Psychiatric Association, 1980) criteria for antisocial personality disorder, level of combat exposure, and development of combat-related post-traumatic stress disorder (PTSD). Results of hierarchical regression analyses indicated that combat exposure level was related significantly to PTSD symptomatology, whereas number of preadult antisocial behaviors was not. However, both combat exposure level and preadult behaviors, which were not correlated significantly, were related significantly to number of adult antisocial behaviors. There were no significant interaction effects. Results were consistent with a theoretical model of PTSD development that emphasizes the role of trauma vs. premorbid characterological factors. In addition, the significant association between combat exposure and adult antisocial behavior indicates that trauma may play a role in the development and/or maintenance of adult antisocial behaviors observed in some Vietnam veterans.