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 (R 2 =.516, p <.0001), or as ml/kgFFM/min (R2 =.127, p =.01). The relationships between peakVO2 and leptin were no longer significant when percent bodyfat was added to the models. In subanalyses by weight groups, peakVO2: 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.