OBJECTIVE: To evaluate the impact on glucose metabolism of a lifestyle program (the Yale Bright Bodies Program) for obese children. RESEARCH DESIGN AND METHODS: Thirteen Bright Bodies and ten clinic-care control subjects who were part of a large randomized clinical trial had 75-g oral glucose tolerance tests at the beginning and end of the 12-month study. RESULTS: Bright Bodies subjects had significantly greater decreases in weight, BMI, and body fat than clinic-care subjects, and the Bright Body subjects' changes in body composition were accompanied by marked improvements in insulin sensitivity (P = 0.009) and glucose tolerance (P = 0.04). CONCLUSIONS: An intensive lifestyle program that successfully reduces body weight and body fat can markedly improve insulin sensitivity and glucose metabolism in obese youth.