Multiple personality is a classical and modern problem in psychiatry. Especially in the United States, it became "epidemic" in 1980S. Its name was now changed to dissociative identity disorder in DSM-IV. This article concerns the psychological interpretation of multiple personality as psychogenic amnesia. The first section briefly reviews dissociation, the basis of the disorder, from the viewpoint of psychopathology. Then dissociation, including the disorder, is examined in the context of cognitive psychology of memory, and it is argued that dissociation is a psychogenic memory disorder accompanied with neurological dysfunction. It follows that multiple personality is a special case of memory disorder. Finally, neurological investigation of the dissociative and multiple personality disorders has shown that the limbic system is implicated in their basic dysfunction. In conclusion, innately high hypnotic susceptibility and severe traumatic experience before and after ego formation both contribute to development of intrapersonal-interidentity amnesia, i. e., multiple personality.