Dissociative identity disorder (DID), previously known as multiple personality disorder (MPD), is a mental disorder on the dissociative spectrum characterized by the appearance of at least two distinct and relatively enduring identities or dissociated personality states that alternately control a person's behavior, accompanied by memory impairment for important information not explained by ordinary forgetfulness. These symptoms are not accounted for by substance abuse, seizures, other medical conditions, nor by imaginative play in children. Diagnosis is often difficult as there is considerable comorbidity with other mental disorders. Malingering should be considered if there is possible financial or forensic gain, as well as factitious disorder if help-seeking behavior is prominent.