Dissociation is one of the most controversial, yet poorly understood, conditions in psychiatry.

Dissociation refers to the disruption (or “split,” in Pierre Janet's word) of the usually integrated consciousness. The symptoms of dissociation have been recorded from the time of antiquity. Many historical cases of spirit or demon possession seemed very much like dissociative disorders in modern eyes. In a mild level of severity, many people can consciously experience brief derealization and depersonalization. Severe dissociative symptoms are usually unconscious and pathological. Among the conditions with dissociation, the most dramatic is dissociative identity disorder, formerly termed multiple personality disorder. The claim that multiple minds can exist within one body had faced challenges from scientific researches due to short of empirical data. Rare in reality, the theatrical inlay of multiple personality disorder, along with other dissociative disorders, attracted waxing and waning public enthusiasm.

Over the past century, surmounting volume of literature has been published in the study of dissociative disorders. However, little conclusion was drawn from well-designed, controlled studies. Historically, dissociation was considered to be part of hysteria (somatoform disorders in DSM nomenclature) due to its lack of physical findings. In recent years, formation of dissociation has been attributed to traumatic experience in childhood. The theory of dissociation being a posttraumatic spectrum disorder has gained some acceptance. There are also neurobiological changes found in dissociative disorders.

DSM-IV-TR allows five diagnoses in the category of dissociative disorders

1. ▶ Dissociative amnesia

2. ▶ Depersonalization disorder

3. ▶ Dissociative fugue

4. ▶ Dissociative identity disorder

5. ▶ Dissociative disorder not otherwise specified (NOS)