Multiple personality syndrome is being diagnosed and treated in the United States in ever increasing numbers. Indeed, it is alleged that the incidence of this bizarre and striking disorder has reached epidemic proportions. Clinician/researchers report each seeing individually more than 100 patients whose minds have split into as many as 60 alter egos. Their case histories are typified by sexual and physical abuse in childhood and some have reached notoriety; in films, like Eve and Sybil and in criminal records, like Bianchi, 'the Hillside Strangler'. But does 'multiple personality' exist? This monograph takes as its point of departure the virtual absence of such patients anywhere except the U.S.A. and even then it is a relatively small number of psychologists and psychiatrists who report the overwhelming majority of cases. The book provides the first comprehensive review of the burgeoning literature from the beginning of the century to the present and covers more than 300 articles and books. It should prove of interest to psychologists, psychiatrists, psychotherapists and social workers and is an invaluable reference for students on courses in clinical and abnormal psychology as well as to practising clinicians and social workers. Following an introduction to a selection of the more notable cases, a number of critical issues are examined in ensuing chapters. These are devoted to problems of definition and differential diagnosis; aetiology; psychophysiological, psychometric and experimental studies; attempts at theoretical explanation and the relationship between MPS, hypnosis and dissociation. The author, a practising clinical psychologist and lecturer in psychopathology, gradually develops the hypothesis that MPS is best explained under the rubric of social role theory. It is argued that MPS is a culture-bound variant of hysterical psychosis occurring in individuals with high 'hypnotisability'. The tentative conclusion is that even if one accepts the reality of MPS it is unhelpful to regard it as a discrete clinical entity, and it is being grossly overdiagnosed.