What is dissociative identity disorder (DID)? Dissociative identity disorder (DID) was formerly called multiple personality disorder. People with DID develop one or more alternate personalities that function with or without the awareness of the person"s usual personality. DID is one of a group of conditions called dissociative disorders. Dissociative disorders are mental illnesses that involve disruptions or breakdowns of memory, consciousness or awareness, identity and/or perception mental functions that normally work smoothly. When one or more of these functions is disrupted, dissociative symptoms can result. These symptoms can be mild, but they can also be severe to the point where they interfere with a person"s general functioning, both in personal life and at work.