Substance abuse among mentally retarded persons, first described 55 years ago, has received little or no attention by specialists in mental retardation. With deinstitutionalization, this problem has reappeared, often followed by victimization (i.e., assault, rape, robbery). In this study the demographic characteristics, family and childhood history, substance use patterns, and substance-related problems of 40 mild mentally retarded persons are compared with those of 40 mild mentally retarded persons without substance abuse. Similarities with substance abusers who are not mentally retarded are noted. Recommendations for alleviating this serious problem among mentally retarded persons are made.