Hydatidosis, caused by Echinococcus granulosus, is an endemic parasitic disease in Mediterranean countries. The most frequent anatomic locations are liver and lung. Intrathoracic rupture of hydatid cysts situated in the hepatic dome is a serious complication resulting in damage to the pleura, pulmonary parenchyma, and bronchi. From January 1984 to December 1997 we operated on 40 patients with intrathoracic rupture of a hepatic hydatid cyst. Chest roentgenograms showed a shadow of varying size at the base of the hemithorax. Hepatic and thoracic ultrasonography was performed in all cases. The diagnosis of intrathoracic rupture of a liver cyst was confirmed preoperatively in 30 of the 40 cases. Posterolateral thoracotomy was performed in all patients. This transthoracic approach allowed adhesiolysis and treatment of the pleural lesions, pulmonary lesions, and hepatic cyst. Treatment of the diaphragmatic gap is easily done. We performed 15 lobectomies, 10 wedge resections, 16 decortications, and in one patient simple drainage of a voluminous pleuropulmonary and hepatic purulent hydatic collection. The postoperative course was uneventful in 26 cases, but 14 patients had complications, from which 3 patients died. The therapeutic approach depends on ultrasonographic findings. We believe ultrasonography to be the best examination for assessing biliary, hepatic, diaphragmatic, and pleuropulmonary lesions. When an intrathoracic collection is present, thoracotomy must be performed and is sufficient if the biliary tract is safe. An abdominal approach is necessary when biliary duct drainage is required, and it may be sufficient in cases of direct rupture into the bronchi.