Dissociative Identity Disorder (Multiple Personality Disorder) By David Spiegel, MD, Stanford University School of Medicine Reviewed / Revised May 2023 View Patient Education Etiology Symptoms and Signs Diagnosis Treatment Prognosis Dissociative identity disorder, formerly called multiple personality disorder, is a type of dissociative disorder characterized by ≥ 2 personality states (also called alters, self-states, or identities) that alternate.