Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; Processo FAPESP: 07/07731-0 ; Processo FAPESP: 11/05991-0 ; Objective: The aim of this study was to investigate the effects of excess body fat on bone mass in overweight, obese, and extremely obese adolescents.Methods: This study included 377 adolescents of both sexes, ages 10 to 19 y. Weight, height, body mass index (BMI), bone age, bone mineral content (BMC), and bone mineral density (BMD) were obtained by dual-energy x-ray absorptiometry. The results were adjusted for chronological age and bone age. Comparisons according to nutritional classification were performed by analysis of variance, followed by Tukey test. Linear regression models were used to explain the variation in BMD and BMC in the L1-L4 lumbar spinal region, proximal femur, and whole body in relation to BMI, lean mass, fat mass (FM), and body fat percentage (BF%), considering P