The present study examined the effects of substance dependence and posttraumatic stress disorder (PTSD) on perpetration of partner violence. Participants were 72 men and 124 women diagnosed with and/or without PTSD and cocaine or alcohol dependence. Participants were interviewed with the Structured Clinical Interview for the DSM-IV (SCID-IV) and completed the Conflict Tactics Scale-2 (CTS-2). Analyses indicated that participants with comorbid cocaine dependence and PTSD reported the highest frequency of partner violence relative to all other groups. Main effects were also detected for drug dependence and PTSD. Results suggest that substance dependence and PTSD alone are associated with increased violence in couples, and most importantly, the presence of PTSD serves to further potentiate the perpetration of partner violence among cocaine-dependent individuals.