Multiple Personality Disorder (now known as Dissociative Identity Disorder) is one of the most complex disorders of dissociation. The sufferer has two or more split personalities, each with a separate identity. Dissociation is where you feel outside of your body, as if you are floating along in a dream and you are not connecting with reality. This disorder is the worst of all, the sufferer disconnects altogether and each of their personalities has power over their body, thoughts and actions. The different identities have their own age, sex and race. Each identity has its own distinct way of talking, moving and way of thinking.

As each personality takes over, it is called a switch. Sufferers have no or little recollection of the switch happening, what each personality does, or says during it. For example one personality could sustain a cut to the hand, when another personality takes over they have no recollection as to how they got the cut.

Sufferers are prone to alcohol and substance abuse, depression, eating disorders and suicidal tendencies amongst other things.

The cause of Multiple Personality Disorder is thought to be due to sustained and severe abuse as a child, over an extended period of time. There is no cure for this disorder.