Little data exist on the comparison of blood lipids and percent body fat between Down Syndrome and non-DS adults with mental retardation (MR). The following study was undertaken to determine if there were physiological and biochemical differences between these two groups. Subjects included 294 non- DS adults with MR (162 males and 132 females) and 31 adults with Down Syndrome (21 males and 10 females). Level of mental retardation was similar for both groups (males/females, Down vs. non-DS). A two-factor ANOVA with a regression approach was used to analyze the data. Results of the study found that there were no significant differences between the Down Syndrome and non- DS subjects on total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, or percent body fat. The present study suggests that the composition of lipoproteins and storage of body fat are similar in Down Syndrome and non-DS adults with mental retardation, and that the risk for developing coronary heart disease appears to be the same for both groups.