Few studies have examined the relationship between posttraumatic stress disorder (PTSD), substance use disorder, and dissociation. We studied 77 women with current PTSD and substance dependence, classified into high- versus low-dissociation groups per the Dissociative Experiences Scale. They were compared on trauma- and substance-related symptoms, cognitions, coping skills, social adjustment, trauma history, psychiatric symptoms, and self-harm/suicidal behaviors. We found the high-dissociation group consistently more impaired than the low-dissociation group.