Although most individuals with posttraumatic stress disorder (PTSD) demonstrate heightened physiological reactivity to trauma-related cues, many of these individuals do not. The presence of comorbid externalizing disorders is a potential explanation for this inconsistency. This study investigated the psychophysiological reactions to both standardized and idiographic trauma-related cues among male Vietnam Veterans with PTSD only, PTSD and a comorbid substance use disorder (PTSD-SUD), PTSD and comorbid antisocial personality disorder (PTSD-ASPD), PTSD and both comorbid ASPD and SUD (PTSD-ASPD/SUD), and healthy controls. Results showed that the heart rate reactivity of the PTSD-ASPD and PTSD-ASPD/SUD groups failed to exceed that of the No Disorder group during the imagery-based task, and the PTSD-ASPD/SUD group showed less skin conductance reactivity than the other three PTSD groups in response to the standardized trauma cues. These findings implicate ASPD comorbidity in reduced physiological reactivity to trauma reminders in some individuals with PTSD.