OBJECTIVE: To determine whether overweight children have lower physical activity energy expenditure (EE) and fitness levels than non-overweight children. STUDY DESIGN: Twenty-four healthy girls aged 7-10 y were divided into overweight (> 95th percentile weight-for-height) and non-overweight (10-90th percentile) groups. Basal metabolic rate (BMR), sleeping metabolic rate (SMR), 24 h sedentary EE (SEE) and total EE (TEE) were measured by room respiration calorimetry and doubly labelled water. Physical activity EE and physical activity level (PAL) were calculated. Fitness (VO2 peak) was measured by a treadmill exercise test. RESULTS: The overweight group had significantly higher body weight, percent fat, fat mass and fat-free mass (FFM) (P < 0.001). The overweight girls had higher BMR, SMR, SEE and TEE (P < 0.001), but not after adjustment for FFM. Physical activity EE and PAL were not significantly different between groups. After adjusting for FFM or weight, submaximal and peak VO2 were not significantly different between groups. CONCLUSIONS: We conclude that these overweight girls do not have lower physical activity EE or fitness levels than the non-overweight prepubertal girls, however, the rather high body fat of the non-overweight group may have precluded us from finding any differences between groups.