We performed a retrospective study of 19 patients who had been operated on for hepatic hydatid disease with diaphragmatic or transdiaphragmatic (D-TD) thoracic involvement chosen from a total of 444 patients who underwent operations for hepatic hydatid disease. In all cases D-TD involvement was confirmed by ultrasonography, CT, or MRI scan. We propose a new classification (grades 1-5) based on the degree of development of D-TD involvement. Before 1984 exposure was obtained by thoracophrenolaparotomy (nine cases) and later by right subcostal incision. Only four patients required atypical pulmonary resection. In 13 cases the diaphragm was repaired, and all 24 hepatic cysts were treated with total (16 cases) or partial (8 cases) cystopericystectomy. There was no operative mortality, and the most serious morbidity consisted of a biliary fistula and a biliobronchial fistula. For treatment of these patients we recommended right subcostal incision and total or near-total cystopericystectomy as a first choice of surgical technique.