The term "Multiple Personality Disorder" (MPD) has been largely replaced by "Dissociative Identity Disorder" (DID).

As the former name implies, MPD/DID is a mental condition in which 2 or more personalities appear to inhabit a single body. A simple definition of DID is:

"Dissociation is an act of disconnecting, locking the memory or pain in a 'suitcase' and storing the 'suitcase' in the back of the brain. Dissociation Identity Disorder is the phenomena of completely disconnecting oneself from a memory (or memories) and the emotions around the memory(ies), creating a separate identity to hold memories and emotions."

Since the 1970s, therapists who believe in the reality of MPD generally believe it to be caused by very severe abuse during childhood -- violence so extreme that the child cannot absorb the trauma in its entirety. The child dissociates, and creates an alternative personality (a.k.a. "personality state," "alter," "part," "state of consciousness," "ego state," "fragment," "identity.") to handle the abuse. If the abuse continues, additional alters are created as needed. "Trying to escape overwhelming fear and pain by imagining you are somewhere else - or someone else -seems to lay the groundwork for separating off some parts of your identity." ₂

Dissociation itself is a common experience. Most people have observed mild dissociative episodes in which they lose touch with their surroundings. Examples include daydreaming, highway hypnosis, or losing oneself in a movie or book. MPD is viewed by some as an extreme level of dissociation, "which may result in serious impairment or inability to function." ₃

According to therapists who specialize in MPD, the "host" (the victim/survivor's basic personality) is not necessarily aware of the existence of these alters. The abuse memories contained within the alters are not typically accessible to the dominant personality. Various "triggers" can cause one of the alters to emerge and take control of the mental processes of the victim for periods of time. This is called "switching." Control then passes back to the dominant personality or to another alter. This may be sensed by one alter or by the host as if there are entire blocks of missing time. She/he may detect MPD as a result of:

the sudden appearance of new possessions that they cannot recall having purchased,

Some alters create new alters as needed. Others perform a system regulatory function; they determine which alter will be in charge at a given time.

A new term, Dissociative Identity Disorder (DID) was created in 1994 to replace MPD. One of the reasons was that MPD was being thrown into disrepute by many people giving phony demonstrations of alter switching during television talk shows.

MPD specialists generally believe that people "with DID (MPD) may experience any of the following: depression, mood swings, suicidal tendencies, sleep disorders (insomnia, night terrors, and sleep walking), panic attacks and phobias (flashbacks, reactions to stimuli or "triggers"), alcohol and drug abuse, compulsions and rituals, psychotic-like symptoms (including auditory and visual hallucinations), and eating disorders...headaches, amnesia, time loss, trances, and 'out of body experiences.' Some people with DID(MPD)/DD have a tendency toward self-persecution, self-sabotage, and even violence (both self-inflicted and outwardly directed)." They believe that the appropriate therapy involves:

	Many therapists and investigators are skeptical about the widespread natural occurrence of true MPD. They assert that "real" MPD it as a non-existent or extremely rare phenomenon, affecting only a handful of persons in North America. They view almost all cases of diagnosed MPD as having been artificially created by an iatrogenic (physician induced) process. That is, it created by a therapist and their client/patient during therapy, without either recognizing the process. At the same time, skeptics are aware of the suffering of those diagnosed with MPD; they regard MPD survivors as victims of bad therapy. Their cure for MPD is to isolate the patient from the therapist and mutual support groups.
	Some Roman Catholics and conservative Protestant Christians believe that the symptoms of MPD are created by multiple, indwelling demons or "unclean spirits" as mentioned frequently in the Christian Scriptures ( New Testament). The appropriate method of treatment is to exorcise the demons. They would disagree with any therapy that involves actually talking to the demons/alters.
	Finally, a few individuals believe that MPD is a naturally occurring phenomenon, and unrelated to childhood abuse or creation by an iatrogenic process. As one web site describes it, MPD is a gift.

	the increasing numbers of malpractice suits against MPD specialists,
	the increasing numbers of cancellations of MPD therapists' licenses to practice,
	the recent drop in membership of their professional organization, the International Society for the Study of Dissociation (ISSD),
	the decreasing numbers of books on MPD/DID therapeutic methods,