In conjunction with the Mayo Clinic in Rochester, Minnesota, the birth records and school records of all Olmstead County residents born in 1960 and 1961 will be reviewed. All persons with mental retardation will be identified from these sources. Mental retardation (MR) is defined for the purpose of this study, as a fixed cognitive deficit which occurred before age 12 with some impairment of social adaptation. In addition to the specification of the incidence and identification of risk factors for MR in this birth cohort, service utilization by the MR cases will be assessed. Specific services which will be assessed will include medical (psychiatric, neurologic, gynecologic, and surgical), social (group homes, sheltered workshops, and rehabilitative programs), and educational (special program or projects and institutional placements).