One hundred and fifty adolescents between the ages of 13 and 16 years and 20% and 90% overweight will be randomized to one of two treatment conditions: 1) Cognitive-Behavioral Weight Loss Treatment with Peer-Based Skills Training (CBT+PBST) or 2) Cognitive-Behavioral Weight Loss Treatment with Exercise (CBT+EXER). Measures of height, weight, physical activity, diet, and psychosocial functioning will be obtained at baseline, end of treatment, 12 months, and 24 months after randomization. A between-groups t-test will be conducted to evaluate group differences in change in percent overweight between baseline and 24-month follow-up. Hierarchical linear modeling will be used to assess the pattern of weight loss for the two treatment groups across four time points: baseline, end of treatment, 12 month, and 24 month follow-up. Effects of treatment on psychosocial measures will be analyzed using mixed analysis of variance with treatment condition as the between subjects factor and a within subject factor of time. Finally, a series of regression analyses will be conducted to evaluate the role of psychosocial variables, physical activity, and diet, as mediators of treatment outcome.