Obesity blunts catecholamine and growth hormone responses to exercise in adults, but the effect of obesity on these exercise-associated hormonal responses in children is unclear. Therefore, the aim of the present study was to asses the effect of childhood obesity on the counter-regulatory hormonal response to acute exercise. Twenty-five obese children (Ob, BMI> 95%), and 25 age, gender and maturity matched normal weight controls (NW) participated in the study. Exercise consisted of ten two-min bouts of constant cycle-ergometry above the anaerobic threshold, with one-min rest intervals between each bout. Pre, post and 120-min post exercise blood samples were collected for circulating components of the GH-IGF-I axis and catecholamines. There were no differences in peak exercise heart rate, serum lactate and peak VO₂ normalized to lean body mass between the groups. Obesity attenuated the GH response to exercise (8.9±1.1 versus 3.4±0.7 ng/ml in NW and Ob participants, respectively; p<0.02). No significant differences in the response to exercise were found for other components of the GH-IGF-I axis. Obesity attenuated the catecholamine response to exercise (epinephrine: 52.5±12.7 versus 18.7±3.7 pg/ml, p<0.02; norepinephrine: 479.5±109.9 versus 218.0±26.0 pg/ml, p<0.04; dopamine: 17.2±2.9 versus 3.5±1.9 pg/ml, p<0.006 in NW and Ob, respectively). Insulin levels were significantly higher in the obese children, and dropped significantly after exercise in both groups. Despite the elevated insulin levels and the blunted counter-regulatory response, none of the participants developed hypoglycemia. Childhood obesity was associated with attenuated GH and catecholamine response to acute exercise. These abnormalities were compensated for, so that exercise was not associated with hypoglycemia despite increased insulin levels in obese children.