Patients with complex dissociative disorders report high levels of childhood- abuse experiences, clinical comorbidity, functional impairment, and treatment utilization. Although a few naturalistic studies indicate that these patients can benefit from psychotherapy, no randomized controlled trials have been reported with this patient-group. In the current study, 59 patients with Dissociative Identity Disorder (DID) or Other Specified Dissociative Disorders (OSDD) were randomized to 20 sessions of stabilizing group – treatment, conjoint with individual therapy, or individual therapy alone, in a delayed-treatment design. The treatment is based on the manual Coping with Trauma-Related Dissociation (Boon, Steele, & Hart, 2011). The primary outcome was Global Assessment of Functioning (GAF), while secondary outcomes were PTSD and dissociative symptoms, general psychopathology, interpersonal difficulties, and self-destructive behavior. Results indicate medium to large effects on psychosocial functioning and small to insignificant effects on reduction of symptoms and self-destructive behavior. Mixed effect models showed no condition x time interaction, indicating no immediate differences in treatment outcome, but some indication of positive effects in the six months follow-up period.