Of a total of 77 patients affected by hydatid cysts of the liver observed between 1983 and 1988, we examined a group of 25 patients with cysts that had migrated into the thorax. The main characteristic of these patients was the hydatid hepatic cyst, which was situated in the right hepatic lobe in every patient, involving one or more right hemithoracic structures. In 24 patients, there were different combinations of symptoms, but only ten were thoracic. In those with advanced intrathoracic evolution of the hydatid cyst, we not only found a destruction of the hemidiaphragm, but also the presence of pleural effusion, empyema, atelectasis and multiple pleural hydatidosis caused by the development of a cystic fistula in the pleural cavity. Analysis of these instances allowed us to see that ultrasonograms of the liver and roentgenograms of the thorax are often the most sensitive and reliable diagnostic procedures for showing the intrathoracic evolution of the cyst. We believe that the surgical treatment must be carried out with simultaneous right thoracoabdominal access, which, besides exposing the thoracic lesions, also permits adequate treatment of the hepatic hydatid cyst and the possible associated biliary complications.