This prospective, randomized study investigated the effect of exercise on leptin, insulin, cortisol and lipid profiles in obese children. A total of 40 obese boys aged 10 - 12 years with a body mass index (BMI) >or= 30 kg/m(2) were randomly separated into an exercise group (n = 20) that underwent a 12-week aerobic exercise programme and a non-exercise (control) group (n = 20). The BMI, low-density lipoprotein, cortisol, leptin and insulin levels were significantly lower in the exercise group after 12 weeks compared with baseline values, whereas high-density lipoprotein levels were significantly higher. In contrast, in the control group, low-density lipoprotein, cortisol and leptin levels were significantly higher after 12 weeks compared with baseline values while high-density lipoprotein levels were significantly lower. These findings indicate the importance of regular exercise in the regulation of body weight and protection against cardiovascular risk factors in obese children.