There is a high incidence of trauma and posttraumatic stress disorder (PTSD) in people with a diagnosis of psychosis. Sequelae of trauma may affect the ability to engage in both attachment and therapeutic relationships. This study investigated associations between trauma histories, PTSD, attachment styles, and working alliance in a sample of 110 individuals with psychosis and substance misuse. Anxious attachment was associated with number of interpersonal traumas and PTSD reported, but there were no associations between trauma and alliance. There were discrepancies in number of traumatic events reported by care coordinators and patients. The findings of this study highlight the potential use of attachment theory in working with trauma and PTSD in psychosis.