Recently, there has been a dramatic rise in the number of case reports of multiple personality disorder (MPD). The phenomenology of the disorder is described and theories on aetiology are discussed. A review of the recent literature reveals a poverty of information on reliability of diagnosis, prevalence, or the role of selection bias. It is argued that iatrogenic factors may contribute to the development of the syndrome. There is little evidence from genetic or physiological studies to suggest that MPD represents a distinct psychiatric disorder. It is assumed that MPD is an hysterical symptom, and an attempt is made to catalogue the predisposing factors and influences that may lead to the clinical presentation.