The diagnostic features and treatment histories of 11 adolescents with multiple personality disorder (MPD) are presented. Clinical evaluation revealed that the majority of these adolescents manifested extremely variable school performance, disruptive behavior, trances, amnesias, mood swings, sharp changes in personality, apparent lying, voices heard in the head, and depression. All had a history of childhood trauma: Sexual abuse (73%), physical abuse (73%), and emotional abuse (82%). Seventy-three percent had a parent with a diagnosable dissociative disorder; 36% of the mothers had MPD. These adolescents had a mean number of 24.1 alter personalities and appear to have become multiple at a mean age of 3 years, 1 month. All patients had angry protector alters, depressed alters, scared alters, and child alters. Fifty-four percent of these cases have integrated during treatment or are progressing toward integration. The remaining cases dropped out of therapy.