This report presents annual basic descriptive and longitudinal population statistics on people with mental retardation and related conditions in state-operated residential facilities in the United States. Part I presents data on numbers of persons with mental retardation and related conditions, including first admissions, readmissions, releases, deaths, and cost of care. Part II presents statistics on characteristics of persons living in public residential facilities in 1987, such as resident movement, level of retardation, age distribution, medical conditions, activities of daily living, instrumental activities of daily living, and employment status. Part III puts 1988 statistics in the longitudinal context of data gathered since 1950 on state institution populations, resident movement, and costs of care. Facilities are categorized by size and whether or not persons with disabilities other than mental retardation reside there as well. An executive summary analyzes trends in the data. Includes 37 references. (PB)