The extension of a pancreatic pseudocyst into the mediastinum is a difficult clinical and radiographic diagnosis. The chest roentgenogram reveals a retrocardiac mass in a patient with nonspecific upper abdominal and chest complaints. Usually there is a preceding history of alcoholism or pancreatitis. The upper gastrointestinal series often demonstrates typical displacement of the distal esophagus anteriorly and to the left. The value of computed tomography is illustrated. Correct preoperative diagnosis is important for proper surgical treatment, since a mediastinal pseudocyst is best managed without thoracotomy.