A patient with pancreatic pseudocyst of the mediastinum is presented. Weight loss, chest or abdominal pain, and dyspnea are the most frequent symptoms of mediastinal pseudocyst. Chest roentgenogram frequently demonstrates a posterior mediastinal mass, and esophagogram always shows esophageal displacement. The diagnosis is confirmed by computerized axial tomography of the chest and abdomen. Cyst-gastrostomy is the operation of choice for this condition.