Several studies have confirmed that there is a high incidence of obesity among adults with mental retardation (MR) living in the United States. However, there has never been a systematic comparison of the anthropometric characteristics between adults with MR from different countries. The purpose of this study was to compare the body composition levels of 210 adults with MR residing in two different residential settings in the United States and in Germany. Subjects' mean age was 31.7 yr. Skinfold measurements were used to estimate percent body fat (PBF), and height and weight were used to compute body mass index (BMI). Results indicated that PBF was significantly higher among females (P < 0.001); subjects in the institutional setting had significantly lower PBF and BMI levels than subjects in the family setting (P < 0.001); and PBF and BMI levels were significantly higher in subjects from the United States compared with the German subjects (P < 0.001). These findings indicate a need for further investigation into the caloric intake, energy expenditure, lifestyle, and metabolic characteristics of adults with MR living in the United States and Germany.