The following randomized controlled trial will examine the effects of one year of dehydroepiandrosterone and estrogen replacement therapy (DHEA +ERT) on bone mineral density (BMD) and bone marrow composition in adolescents with anorexia nervosa (AN). The investigators will use imaging techniques including dual-energy x-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), visual assessments of magnetic resonance imaging (MRI) data, MR relaxometry and magnetic resonance spectroscopy (MRS) to measure bone mineral density and evaluate bone marrow composition. The investigators will also collect serum to measure hormonal mediators of the changes observed in both bone density and bone marrow composition, including adrenal and gonadal steroids, insulin-like growth factors, growth hormone, and ghrelin, adiponectin, and leptin.