This study will assess changes in dietary intake and eating behavior in 110 extremely obese adolescents who undergo bariatric surgery as part of the main Teen-LABS study. These individuals will be recruited from one of 4 Teen-LABS sites: Baylor College of Medicine, Cincinnati Children's Hospital Medical Center, University of Alabama at Birmingham, and the University of Pittsburgh Medical Center. Changes in bariatric surgery patients will be compared to those of 110 obese adolescents treated with a lifestyle modification program designed to produce an 8% weight loss. These individuals will be recruited from a study at the Children's Hospital of Philadelphia (PI: Robert Berkowitz, M.D.) which will be ongoing at the same time and will include the same measures as those proposed in this application.