Osteoporosis is a frequent complications of anorexia nervosa (AN). The etiology of osteoporosis in AN is multifactorial. Multiaxial hormonal disturbances and chronic undernutrition cause decrease or the lack of increase of bone mineral density (BMD), expected in adolescence. Both processes result from increased resorption and insufficient bone formation and/or mineralization. Decreased BMD persist in adult patients with a history of AN in the adolescence. There are no guidelines concerning treatment of osteoporosis in AN. The authors present review of the literature concerning bone metabolism in AN.