Osteoporosis is a common and very serious complication of anorexia nervosa. It affects these patients, both males and females, at very young ages. This loss of bone mineral density begins quickly, soon after the onset of the eating disorder. It is one of the rare medical complications of anorexia nervosa which may result in irreparable harm, even if there is successful nutritional rehabilitation and weight restoration. Nevertheless, notwithstanding its high importance, there is a paucity of evidence-based medicine to guide the optimal approach to diagnosis, prevention, and treatment. This paper attempts to inform clinicians taking care of these patients about a reasonable and measured approach to this problem, while the field awaits more definitive medical literature.