Severe dissociative disorders (DD) are associated with high levels of impairment, treatment utilization, and treatment costs, yet relatively little systematic research has focused on treatment for these challenging patients. The goal of this naturalistic observational 30-month follow-up study of an international sample of patients with dissociative disorders was to determine if treatment provided by community providers was associated with improvements in symptoms and adaptive functioning. The patients were diagnosed with dissociative identity disorder (DID) and dissociative disorder not otherwise specified (DDNOS). The patients and their therapists completed surveys at study entry and at 6-, 18-, and 30-month follow-up. At the 30-month follow-up, 119 of the original 226 patients completed the surveys. According to patients’ reports, they showed decreased levels of dissociation, posttraumatic stress disorder symptoms, general distress, drug use, physical pain, and depression over the course of treatment. As treatment progressed, patients reported increased socializing, attending school or volunteering, and feeling good. According to therapists’ reports, patients engaged in less self-injurious behavior and had fewer hospitalizations as well as increased global assessment of functioning scores (American Psychiatric Association, 2000) and adaptive capacities over time. These results suggest that treatment provided by therapists who have training in treating DID/DDNOS appears to be beneficial across a number of clinical domains. Additional research into the treatment of DD is warranted.