Plasma lipid, glucose, and insulin levels were measured from 26 patients with Prader-Willi syndrome (16 with the chromosome 15q deletion and 10 with normal chromosomes) and 32 obese, normal individuals. The average percentage of ideal body weight (IBW) for the former group was 175.6 ± 68.0, compared to 150.3 ± 43.8 for the latter. Fasting plasma lipid, glucose, and insulin levels were not significantly different between the two groups. No significant correlations were found among the three measurements in patients with PWS (deletion or nondeletion) or obese individuals and either age or percentage of IBW. Both insulin and glucose levels were higher in the PWS group, while only insulin levels were higher in the obese group compared with normative laboratory standards. Our study supports previously reported lipid, glucose, and insulin data in PWS and obesity.