Dissociative identity disorder Dissociative identity disorder ( DID ), previously known as multiple personality disorder ( MPD ) and colloquially known as split personality disorder ( SPD ), is a mental disorder characterized by the maintenance of at least two distinct and relatively enduring personality states . The disorder is accompanied by memory gaps beyond what would be explained by ordinary memory issues. The personality states alternately show in a person's behavior; however, presentations of the disorder vary. Other conditions that often occur in people with DID include post-traumatic stress disorder , personality disorders (especially borderline and avoidant ), depression , substance use disorders , conversion disorder , somatic symptom disorder , eating disorders , obsessive–compulsive disorder , and sleep diso...