The present study was performed using indirect calorimetry to test the hypothesis of a reduction of the basal energy expenditure in obese prepubertal children. The obese and control children studied were comparable regarding age, height and fat-free mass (FFM). Total weight and body fat percentage were significantly greater in the obese children. Plasma insulin and glucagon concentrations were significantly higher in obese than in control children. In the two groups of children the basal metabolic rates (BMRs) were comparable in both absolute values and values adjusted for FFM, age and gender utilizing the multiple regression analysis. The most important variable to predict BMR was FFM, followed by age. BMR was significantly correlated with FFM, both for obese and control children, and also when the two groups were combined. In conclusion, our data do not support the idea that a child's obesity is maintained by increased metabolic efficiency at least in basal conditions.