We measured body composition, basal metabolic rate (BMR), and total energy expenditure in 28 nonobese and 35 obese adolescents aged 12-18 y using indirect calorimetry and the doubly labeled water method. BMR was highly correlated with fat-free mass in both the nonobese and obese groups (r = 0.77 and 0.84, respectively). BMR adjusted for fat-free mass was significantly greater in males than females and in the obese subjects. Total energy expenditure was significantly greater in the obese than nonobese cohort but ratios of total energy expenditure/BMR were not significantly different in the two groups (1.79 +/- 0.2 versus 1.68 +/- 0.19, nonobese and obese males and 1.69 +/- 0.28 versus 1.74 +/- 0.19 nonobese and obese females, respectively). These data indicate that BMR and total energy expenditure are not reduced in the already obese adolescent. Therefore, reduced energy expenditure cannot be responsible for the maintenance of obesity in adolescents.