Adolescents and young adults with anorexia nervosa (AN) are at high risk for low bone mineral density at a time when healthy adolescents are rapidly accruing bone, with implications for peak bone mass and fracture risk in later life. They are also deficient in insulin-like growth factor 1 (IGF-1), the bone trophic factor made in the liver in response to growth hormone (GH), despite elevated levels of growth hormone. It is possible that deficiency of insulin-like growth factor 1, a hormone very important for the maintenance of skeletal integrity, may contribute to the severe osteopenia seen in anorexia nervosa. The physiologic effects of recombinant human insulin-like growth factor 1 (rhIGF-1) treatment in adolescents and young adults with anorexia nervosa have not been studied. The goal of this proposal is to investigate the effects of recombinant human insulin-like growth factor 1 on bone density and bone microarchitecture in adolescent girls and young adult women with anorexia nervosa over a 6 month period. We hypothesize that adolescent and young adult anorexia nervosa patients, being insulin-like growth factor 1 deficient, will respond to exogenously administered recombinant human insulin-like growth factor 1 with elevations in biochemical indices of bone turnover and an increase in bone density and improvement in bone structure, or maintain bone density (in contrast to the decrease in bone density expected in adolescent girls and women with anorexia nervosa who are not treated).