Osteoporosis is now established as one of common and early physical complications of anorexia nervosa (a.n.). The etiology of bone demineralisation in a.n. is multifactorial. Various studies suggest that long duration of a.n. and amenorrhea, early onset of illness and amenorrhea, low body mass index, low lean and fat mass in body, inadequate calcium, vit D3 and protein intake, hypoestrogenemia and hypercortisolemia are related to decreased bone mineral density (BMD). The severity of bone mass deficit is sufficient in some patient to result in pathological fractures of spine, hip or long bones. Fractures may occur after 7-15 years of a.n duration. Crucial for increase of BMD is restoration of weight and resumption of menses. The issue of reversibility of osteopenia, indications and methods of treatment for patients with decreased BMD are of clinical importance.