One of the most curious syndromes is misidentification of self in which the individual perceives himself or herself as another person while being able to explain the loss of the original identity. The authors illustrate the possible changing nature of delusional misidentification and the fact that the process may be not only one of quality, but sometimes one of degree. The transitory delusion involving the total loss of personal identity is not a common event, and misidentification syndrome is not restricted to a single, specific illness. Such processes occur in the course of a variety of psychotic reactions, sometimes in association with organic brain deficit. Recognizing these processes may be helpful in accurate diagnosis; in considering such conditions as psychosis of whatever type, multiple personality disorder, and other amnesia and fugue states; and in understanding the person's psychopathology. Two cases are presented to illustrate a process that the authors call the Riel Phenomenon, a delusion in which a person believes that he or she has assumed a totally different identity. This mental state is differentiated from amnestic, fugue, or other dissociative states in which there is no recollection of prior identity or in which the individual recognizes only gaps of consciousness. 16 references (Author abstract modified)