A thirty-five-year-old married woman suffered for two years from a recurrent, intrusive concern that her husband had been replaced by an impostor. She had similar worries that her parents, her cat, and even the city in which she lived had been replaced by duplicates. Careful psychiatric and psychological examination failed to demonstrate any psychosis. Her speech and thought processes were characterized by extreme attention to detail, and she pressed continually for reassurance. Soon after the patient left home for college at age seventeen, she was hospitalized because she developed ritualistic habits, compulsive hand-washing, and other