The prevalence of psychiatric disorders in a large residential population (N = 1,273) of individuals with mental retardation was examined. We found that the point prevalence rate for dual diagnoses based on DSM-III-R criteria was 15.55% (n = 198). Rates for specific psychiatric disorders were also provided by level of retardation and sex. Results were compared to similar epidemiological studies and discussed in light of factors hypothesized to affect diagnosis of psychiatric disorders among individuals with mental retardation.