A 33-year-old woman had a 4-day history of severe left shoulder and pleuritic chest pain. The pain progressed and became epigastric and associated with vomiting. The patient reported a 2- year history of similar episodes that were not as severe or as prolonged as this episode. At prior evaluations, the patient was told that the diagnosis was irritable bowel syndrome. The patient was visibly anxious, her temperature was 37.8°C, and her pulse rate was 150 beats/min. On physical examination, the patient had reduced air entry in the left lung base and had left upper quadrant abdominal tenderness. Her white blood cell count was 14 800/μL, and her hemoglobin was 12.9 g/dL. Other laboratory test results were normal. A chest x-ray film showed decreased excursion of the left hemithorax but no other abnormality. With no pleural cause for the limited diaphragmatic excursion, we performed a computedtomographic scan of the abdomen (Figure 1). It showed an abdominal mass that we thought was arising from the stomach, so we performed an endoscopy. We saw an extrinsic mass compressing the stomach and 2 small submucosal masses in the prepyloric region. Based on the findings, the patient was taken to the operating room, where we identified a flaccid tumor in the lesser sac abutting and densely adherent to the left lobe of the liver, the gastroesophageal junction, and the central tendon of the diaphragm (Figure 2).