This study analyzes whether cardiorespiratory exercise performance is impaired in obese children when parameters of aerobic exercise function are used that are independent of body mass. Twenty-one obese patients (mean age 11.6 ± 2.5 years) were studied and compared with 22 normal controls of the same age range (11.4 ± 2.2 years; p = .78). All participants underwent square wave exercise testing on a treadmill for 6 min (speed 5 km/hr, inclination 4%). The oxygen deficit, calculated as ml·min·kg⁻¹, was expressed as a percentage of the total oxygen cost for the 6-min exercise bout (also expressed as ml·min·kg⁻¹). Oxygen deficit amounted to 7.2 ± 1.9% in the obese patients and was not significantly different (p = .25) from the normal controls (6.6 ± 1.1%). The similar values for O₂ deficit in obese patients compared with normal controls shows that cardiovascular fitness in obese patients is normal when parameters of aerobic exercise function are not normalized per kg of body mass.