It have been studied 90 children (obese 73, non obese or control 17), trying to analyze the following parameters: mean and standard deviation values, its circadian rhythms and relation between cortisol and insulin, correlation between both hormones and anthropometric parameters of obesity and sexual influence with all the studied parameters. The plasmatic cortisol values were higher in male, obese (180.4 +/- 11.2 ng/ml) and control (377.5 +/- 49.2 ng/ml) children. The plasmatic insulin values higher in obese children (55.3 +/- 9.5 microU/ml) verifying the hyperinsulinemia observed in obesity. There was not correlation between cortisol and insulin values with body fat. All the children showed cortisol and insulin circadian rythm. In the groups of obese children the cortisol circadian rythm was similar to the control one. However, the insulin circadian rythm was disturb. So, the acrophase was delayed two hours when male and female were analyzed all together and only one hour in the obese female group. The acrophase of cortisol and insulin rhythms in obese group is delayed in relation with the degree of obesity. The circadian rhythms of cortisol and insulin, in both obese and control groups, are not dependent. The duration of obesity do not have any relation with the mentioned alterations.