Osteoporosis is common in anorexia nervosa. It places these patients at increased lifetime risk for fractures. Bone loss may never recover completely even once weight is restored. The strongest predictors of osteoporosis include low body weight and amenorrhea. Loss of bone density can occur rapidly and very early in the course of anorexia nervosa. The etiology of bone loss in the patient with anorexia nervosa is multifactorial. In addition to reduced estrogen and progesterone, excess cortisol levels and low levels of insulin growth factor (IGF-1), a correlate for bone formation, are observed. Dual energy x-ray absorptiometry screening is important to assess bone density. However, successful treatments to reverse bone loss, in those with anorexia nervosa, are lacking. Early diagnosis and treatment of anorexia nervosa are paramount to prevent initial weight loss and subsequent loss of bone.