The purpose of this study was to determine the incidence of obesity among 364 adults (mean age, 36.8 years) with mental retardation living in four residential settings. Skinfold measurements were used to measure adiposity. Results indicated that rates of obesity were significantly higher among females, subjects with severe mental retardation had the lowest overall rates of obesity, and the institutional group had the lowest incidence of obesity. These findings indicate a need for more investigation into the caloric intake and energy expenditure of adults with mental retardation, specifically focusing on level of retardation and living arrangement.