Dissociative Identity Disorder (DID), as defined by the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM), is a psychiatric diagnosis that describes a mental illness in which a single person displays multiple distinct identities or personalities, each with its own pattern of perceiving and interacting with the environment. The diagnosis requires that at least two personalities routinely take control of the individual's behavior with an associated memory loss that goes beyond normal forgetfulness; in addition, symptoms can not be due to substance abuse or medical condition. Earlier versions of the DSM named the condition multiple personality disorder (MPD) and the term is still used by the ICD-10.

DID is a controversial diagnosis and condition, with much of the literature on DID being generated and published in North America, to the extent that it was regarded as a phenomenon confined to that continent. Full Text Even within North American psychiatrists, there is a lack of consensus regarding the validity of DID, . Piper and Mersky consider it a culture bound, iatrogenic condition Full Text and the DSM states that there is controversy over the accuracy DID patients' reports, because childhood memories may be subject to distortion and some people with DID may be vulnerable to suggestive influences. Yet the DSM also states that the reports of DID patients of their past history of sexual or physical abuse are often confirmed by objective evidence and that individuals responsible for the actions of physical and sexual abuse might be prone to distort or deny their behaviors. Practitioners who accept DID as a valid disorder have produced an extensive amount of literature and research originating outside North America has appeared in recent years that documents the epidemiology of the condition in a far greater variety of countries and cultures.