This 2 arm study will assess the effect of Xenical on body mass index (BMI)in obese or overweight adolescents. Patients will be randomised into one of 2 groups; both groups will undergo a regimen of mildly hypocaloric diet and physical exercise, but one group will also receive Xenical 120mg po tid. The anticipated time on study treatment is 1 year, and the target sample size is <100 individuals.