This article describes a group weight control project with severely obese adolescent girls in a medical setting. Behavior modification and nutritional principles were utilized with peer group ...interaction. Significant others were included through separate group meetings. This approach produced small amounts of net weight loss for the girls. The drop-outs continued to have a net gain. As a treatment method, this program was more effective for these girls than previous individual clinic contacts had been. When losing weight, the girls tended to use behavior modification techniques more often, and their diets became more adequate nutritionally. Development of group cohesion was tenuous and temporary. Girls who were functioning more independently appeared to do better in weight loss. Disinterested significant others were preferable to nonsupportive ones. A predictive factor was identified, the girls' perception of control. This was measured by the I-E test. Those with a more internalized perception of control were more likely to continue with the program and more likely to lose weight. Because the patient group was small, findings are tentative. However, this program helped to define particular areas that deserve further exploration.