Multiple personality disorder or MPD is a mental condition in which two or more distinct identities or personality states alternate in controlling the patient's consciousness and behavior. It is a mental disturbance classified as one of the dissociative disorders . It is also known as dissociative identity disorder (DID).
MPD is often raised as an insanity defense in criminal cases. State laws governing defense based on MPD differ. For example in Ohio, the actions of a person with a multiple personality disorder are conscious and voluntary within the meaning of RC § 2901.21, although at the time of the act s/he was dissociated from her primary personality and in the state of consciousness of a secondary personality, when the evidence fails to establish the secondary personality was either unconscious or acting involuntarily. It is immaterial whether the person was in one state of consciousness or another, so long as being in the personality then controlling his/her behavior, s/he was conscious and his/her actions were a product of his/her own volition. [State v. Grimsley, 3 Ohio App. 3d 265, 444 N.E.2d 1071 (1982)].
The following is an example of a case law on mixed personality disorder:
The district court adopted the appointed examiner's extensive diagnosis of appellant. Appellant is diagnosed with exhibitionism, which is defined as recurrent, intense, sexually arousing fantasies, urges, or behaviors involving the exposure of one's genitals to an unsuspecting stranger. He also suffers from attention-deficit hyperactivity disorder, alcohol dependence, marijuana dependence, and probably substance abuse. He is characterized by features of several personality disorders, most predominately multiple traits described as "cluster B" personality disorders, which include anti-social, borderline, narcissistic, histrionic, passive-aggressive, and "negativistic" personality disorders. These are defined as multiple personality disorders not otherwise specified, or a mixed personality disorder. [In re Larkin, 1999 Minn. App. LEXIS 833, 5-6 (Minn. Ct. App. 1999)].