A patient presented to our hospital complaining of chest pain and fever for two days. A chest x-ray revealed opacity of the left hemithorax suggesting massive pleural effusion. Thoracocentesis under the guidance of chest sonography aspirated a foul-smelling muddy-brown fluid. During a left posterolateral thoracotomy for decortication, a gangrenous proximal third of the stomach was found within the left thoracic cavity incarcerated in the left hemidiaphragmatic defect. The stomach contained muddy-brown, foul-smelling necrotic gastric contents which made us realize that the empyema we aspirated before was actually the contents of the stomach. A partial gastrectomy of the proximal gangrenous stomach anddecortication of the pleura was performed and the ruptured diaphragm was repaired. An incarcerated diaphragmatic hernia of the stomach is a surgical emergency. We should keep a high index of suspicion of the diagnosis and it should be included as a differential diagnosis in the case of intestinal obstruction with a history of trauma. Aggressive surgical treatment may save the patient's life.