Anorexia nervosa (AN) is a potentially life-threatening eating disorder characterized by an intense fear of gaining weight and a distorted body image. Although AN is a psychiatric illness, it is also very important from a pediatric perspective, as it can cause major medical complications in every organ system in the growing and developing body. The medical complications of anorexia nervosa may endanger the patient in several ways, and the severity of medical complications may be underestimated. Pediatricians should be aware of the possibility of medical complications in adolescent patients who have an eating disorder and understand that, if not managed correctly, such complications may be fatal. This case report describes the vast number of medical complications that can be observed in an adolescent due to an eating disorder.