Osteoporosis is present in over half of all patients with anorexia nervosa. Bone loss often occurs at a young age and may persist even after recovery, predisposing patients to debilitating spinal crush fractures. The pathogenesis of bone loss in anorexia nervosa is not completely understood and may result from a number of mechanisms, including estrogen deficiency, inadequate vitamin and calcium intake, and nutritional effects on bone formation. Recent studies demonstrate that estrogen itself is inadequate to increase bone density in a majority of patients with anorexia nervosa and suggest that nutritionally dependent factors such as insulin-like growth factor-I (IGF-I), a potent bone trophic hormone, may be important in maintaining bone mass. IT is hoped that new anabolic strategies to increase osteoblast function will become available in the future. In the interim, weight gain, restoration of gonadal function, and calcium supplementation remain the cornerstones of treatment in this disease.