The effectiveness of the adolescent obesity intervention SHAPEDOWN was evaluated for 15 months through a randomized experimental design study. Test groups (no. = 37) participating in the intervention were compared with a no-treatment control group (no. = 29) at four sites in northern California. The program employs a variety of cognitive, behavioral, and affective techniques adapted to make successive small modifications in diet, exercise, communication, and affect that are sustainable. Very-low-calorie or restrictive diets are avoided in the program. Parents are instructed on strategies for supporting their adolescents' weight-loss efforts. Participation in the group application of the program was associated with significant improvement in relative weight, weight-related behavior, depression, and knowledge of weight management concepts at post-treatment and at 1-year follow-up. Self-esteem increased significantly regardless of condition. Change in relative weight for the test group was -9.9 +/- 14.9% (mean +/- standard deviation) and for the control group was -0.10 +/- 13.2%. At month 15 of the study period, weight change in the test group compared with the controls was -5.15 kg. For all subject variables examined in the test group, mean change in relative weight at 1-year follow-up was negative, suggesting that none of the characteristics examined contraindicate program participation among obese adolescents seeking care. Drop-out rate was 16%. The study suggests that the program produces significant long-term outcomes in obese adolescents and is transferable to a variety of settings.