Research on obese adults has shown that their ventilatory dynamics differ from normal weight adults; however, the ventilatory dynamics of obese and non-obese children have never been documented. Thus, the ventilatory responses of 73 overweight youth (BMI >85th percentile) were compared to 73 age, sex and height-matched normal weight youth (BMI <85th percentile), during 15 min of rest and steady-state exercise at 4, 5.6 and 8 kph. Overweight youth had higher oxygen uptakes (VO2 mL/min), ventilation (VE), tidal volume (V (T)), frequency (f (R)), physiological dead air space (V (D)) and V (D)/V (T) ratios than normal weight youth (P < 0.02); however, end-tidal CO(2) (P(ET)CO(2)), VE/VO2 and VE/VCO2 were similar. Inspiratory drive (V (T)/t (i)) was greater for overweight youth at rest and during exercise. The correlation between P(ET)CO(2) and inspiratory drive was significant for the overweight group at 5.6 and 8 kph (r = 0.23-0.44), but not significant for the normal weight youth (r = -0.04 to 0.10). The greater drive, respiratory frequency and physiologic dead air space of overweight youth suggest that their adiposity modifies ventilation dynamics during exercise. However, the modifications appear to meet the metabolic demands of exercise.