To evaluate the effectiveness of highly purified glucomannan in childhood obesity a study has been carried out in 23 obese children (12 boys and 11 girls, aged 5.2-15.8 years), with excess weight of 51 +/- 16%, treated with 2-3 caps twice a day of glucomannan fibres (DICOMAN 5:2-3 gr/die), and in 30 obese children (aged 5-18 years) with excess weight of 51 +/- 10%, studied as controls. After a three-days food recall, a balanced diet with adequate caloric intake was provided to all obese children. In all patients before and 2-4 months after the auxological data (weight, height, weight excess) and laboratory data (serum levels of cholesterol, HDL, triglycerides, glucose, fructosamine, glycosylated hemoglobin, RBC, WBC, hemoglobin, iron, calcium, Cu and Zn) have been determined. Excess weight and triglycerides levels were significantly decreased in treated obese patients than in obese controls 4 months after the beginning of the study. A decrease of cholesterol levels was also observed in treated obese patients, but not in controls, whereas serum iron, calcium, copper and zinc persisted unchanged. No important side-effects were observed in treated patients. On the basis of our results highly purified glucomannan fibres may be employed with effectiveness in obese and dyslipidemic children together with diet.