patients suffering from anorexia nervosa (AN) have a litany of medical complications which are commonly present as part of their eating disorders. Almost every body system can be adversely, affected by this state of progressive malnutrition. Moreover, some of the complications can have permanent adverse effects even after there is a successful program of nutritional rehabilitation and weight restoration. Within this article we will review all body systems affected by AN. There is also salient information about both, how to diagnose these medical complications and which are the likely ones to result in permanent sequelae if not diagnosed and addressed early in the course of AN. In a subsequent article, the definitive medical treatment for these complications will be presented in a clinically practical manner.Anorexia nervosa and bulimia are both inherently associated with many different medical complications. This review article is part one of a planned three part series of articles in this regard. We will focus solely on the medical complications associated with restricting anorexia nervosa. Part two of this series will be devoted to the medical complications associated with bulimia nervosa and, the third paper will discuss the treatments currently available for the medical complications of both anorexia nervosa and bulimia. Some of this information is based on experienced clinical opinion.