For 3 years, from 1966-68, data were collected representing the behavioral, social, and medical characteristics of over 20,000 retardates, the resident population of 22 state institutions for the mentally retarded in 13 western states. The data were returned to the institutions where they stimulated research, program development, evaluation, and inter- and intrainstitutional cooperation. Research uses and administrative uses of the data are discussed and illustrated by studies comparing phenylketonurics and mongoloid retardates with matched retarded controls, studies presenting characteristics for subgroups of mongoloids, and others. Twelve graphs and 40 tables present descriptive data and statistical analyses. (LE)