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. Also, the sample overall evidenced relatively high levels of dissociation, indicating that even in the presence of recent substance use, dissociation remains a major psychological phenomenon. Indeed, the high-dissociation group reported stronger expectation that substances could manage their psychiatric symptoms. The high-dissociation group also had more trauma-related symptoms and childhood histories of emotional abuse and physical neglect. The discussion addresses methodology, the "chemical dissociation" hypothesis, and the need for a more nuanced understanding of how substances are experienced in relation to dissociative phenomena.