The purpose of this investigation was to determine the percent body fat of 553 institutionalized mentally retarded adults, ages 18 to 40 yrs, from the Denton State School in Texas. The subjects included 343 males and 210 females. Their percent body fat was estimated with generalized regression equations. Body density for males was measured by the sum of three skinfolds, two girths, and age. Body density for females was measured by the sum of three skinfolds and age. The results from this study revealed that 45.2% of the males and 50.5% of the females were obese. The percent body fat of the female subjects was significantly greater than that of the male subjects. A post hoc analysis revealed that profoundly mentally retarded subjects had significantly lower percent body fat than those subjects functioning at the severe and mild levels. These findings indicate a serious need for more investigation of the caloric intake and expenditure of this population in an institutional environment.