A 15-YEAR-OLD GIRL with Down syndrome and severe developmental retardation came to the hospital with nausea and intractable vomiting of 24 hours' duration. The patient's initial examination results were unremarkable except for minimal abdominal tenderness. Her white blood cell count was 11 000/mm3. A nasogastric tube was placed with the return of "coffee-ground" material and the tube was subsequently removed. She was admitted to the hospital with the presumptive diagnoses of viral gastroenteritis and Mallory-Weiss tear. During the subsequent 16 hours, the patient developed progressively worsening tachycardia, tachypnea, fever, and generalized abdominal pain, which prompted an evaluation by the surgical team. During the initial surgical consultation, she was noted to have a temperature of 39.5°C, a heart rate of 136 beats per minute, and her blood pressure was 100/63 mm Hg. Physical examination of the abdomen revealed diffused abdominal tenderness with generalized peritoneal irritation. The abdominal and chest radiograph films obtained at that time are shown in Figure 1and Figure 2.