A serious shortage of psychiatrists trained to care for mentally retarded patients exists. Based on a successful program that has been in place for more than a decade, the authors offer guidelines for training psychiatric residents in the diagnosis and treatment of mental illness in mentally retarded persons. They describe a model curriculum and suggest ways to modify existing four-year curricula. Special diagnostic skills for working with this population, such as posing questions in concrete terms and ruling out the effects of disabilities like seizure disorders, are reviewed. Important treatment issues include knowing the side effects of neuroleptics and understanding the stages through which families and other caregivers pass in accepting a person's mental retardation.