Osteoporosis has been shown to be a relatively common complication of anorexia nervosa (AN). So far the exact mechanisms which are implicated are not fully clarified. Several factors such as malnutrition, reduced body weight, amenorrhea, and hypercortisolaemia seem to be involved. There is a strong relationship with the duration of amenorrhea and--in some studies--with the age of onset. Osteoporosis is for a long time a "silent" disease and the first symptoms such as back pain, loss of height, kyphosis, and fractures are late complications. Therefore, routine screening methods for bone density measurements should be established. The most accurate is the dual energy X-ray absorptiometry (DEXA). Therapeutically the primary aim should be to reach restoration of both normal body weight and regular menses. As AN is a chronic disease clinicians should be aware of the dangers of osteoporosis and start with the treatment and/or prevention of osteoporosis early. However, at this stage it is difficult to provide an evidence-based management plan for osteoporosis in AN. Hormone replacement therapy (HRT) as well as calcium and vitamin D-supplementation are under discussion, however, further controlled investigations are warranted.