Between 1970 and 1985, seven patients were referred to us for surgical treatment of simultaneous hydatid cysts in the liver and the chest. Their mean age was 45.4 years (age range, 23-73 years), and they represented 46% of patients with hydatid cysts in the liver and thorax. Three patients had hepaticopleural involvement, and 3 patients had symptoms of pulmonary origin. In a single patient, only the diaphragm was involved along with the liver. Liver scintigraphy and ultrasonography were equally helpful in delineating the extent of the disease, but computed tomographic scanning is now the method of choice. The operations were through a thoracolaparotomy in 3 patients and a thoracotomy alone in 3 patients. A single patient had a thoracotomy with a transdiaphragmatic laparotomy. Complete drainage or excision of hydatid cavities was accomplished in all patients. Hydrogen peroxide instilled into the cysts was satisfactory for control of spread potentially secondary to possible intraoperative spillage. There have been no postoperative deaths. Follow-up has ranged from 6 months to 8 years, and 2 patients had relapsing hydatid disease 3 years postoperatively. These results suggest that, when hydatid disease of the liver is complicated by transdiaphragmatic extension and simultaneous pleural or pulmonary cysts, early surgical repair is indicated. Complete drainage and cyst excision are recommended.