The pseudocyst of the pancreas is a frequent complication of acute pancreatitis. However to intrathoracic localization remains exceptional. A case of acute respiratory insufficiency in a 66-year-old man in whom artificial ventilation was required for such a complication is reported. This case stresses the difficulty often encountered for the differential diagnosis of these liquid tumors. The clinical signs are variable and non specific, especially in case of absence of any history of pancreatitis. The radiographic studies, in particular ultrasonography and CT-scanner defines its liquid nature and its connections. Endoscopy examination confirms its retro-oesophageal extension due to the migration through the oesophageal hiatus. Only the percutaneous needle aspiration of a collection or an associated pleural effusion confirms the diagnosis by the high content of amylases. The treatment of this type of localisation is surgical and essentially consists of an internal derivation.