The relationship between peak aerobic fitness (peakVO2) and plasma leptin was assessed in 25 normal (BMI < 85th %tile) and 25 overweight (BMI > 85th %tile) youth, ages 7-17 years. In the overall analysis peakVO2 was related to leptin when expressed in mL/kg/min (R2 = .516, p < .0001), or as ml/kg(FFM)/min (R2 = .127, p = .01). The relationships between peak VO2 and leptin were no longer significant when percent bodyfat was added to the models. In subanalyses by weight groups, peak VO2: leptin relationships were not evident for normal weight, but remained for overweight youth. In conclusion the relationship between aerobic fitness and leptin in youth is dependent upon weight status.