Mediastinal pseudocysts of internal pancreatic fistulas are rare as a cause of bilateral pleural effusions even in relapsing pancreatitis. We describe a 38-year-old man with recurrent bilateral pleural effusion as a complication of a pancreatic pseudocyst. Extension of a pancreatic pseudocyst into the posterior mediastinum was clearly identified by endoscopic retrograde cholangiopancreatogram and subsequent computed tomography scan of the abdomen and chest, and the complication was successfully treated by surgical management. We stress the importance of definite assessment of the communication of pancreatic pseudocyst with mediastinum in patients with pancreatitis who develop recurrent pleural effusions.