We report a rare case of gastric perforation in a 13-year-old boy with anorexia nervosa. He was admitted to our hospital with the chief complaint of body weight loss. He had lower abdominal pain after 2 days. An abdominal CT revealed diffuse peritonitis. At laparotomy, the stomach was dilated and perforated. Postoperatively, the patient suffered from malnutrition. We monitored electrolytes, minerals, and fluids closely before and during the initiation of feedings to prevent morbidity and mortality associated with refeeding syndrome. We present an extremely rare complication that relates to this phenomenon, describing an acute gastric dilatation that led to gastric necrosis and perforation through an unusual mechanism in an extremely anorectic teenager during hospitalization for refeeding.