This article presents the first comprehensive review of studies of alcohol and illicit substance use in mentally retarded individuals, including prevalence, and recommendations for assessment and treatment. Mentally retarded persons appear to use/abuse alcohol at about the same rate as their noncognitively-impaired counterparts, and illicit drugs at moderately lower rates. However, little is known regarding which assessments and interventions are most effective in this population, given the absence of published treatment outcome studies and case examples. This is particularly disconcerting as detrimental consequences resulting from substance use have been identified in mentally retarded samples. Anecdotal data suggests that treatment for these individuals require modifications of existing empirically-derived substance abuse interventions to accommodate their unique needs.