The aim of this retrospective study was to determinate whether the ultrasonic dissector (U.S.D.) is a major advance over existing methods in hepatic surgery. Between 1983 and 1989, we performed 70 hepatectomies "réglées". Twenty seven patients were operated because of benign lesions and 43 patients because of malignant tumours. Transparenchymal approach using "Kellyclasy" or digitoclasy with control of the hilar vessels was carried out 39 times. U.S.D. was used 31 times. No mortality was observed during operating time or post-operative period. The postoperative morbidity was not attributable to the use of the U.S.D. On the whole, U.S.D. has modified neither the amounts of blood loss nor the duration of hilar clamping. However the use of U.S.D. presents 3 advantages: it allows sometimes to perform hepatectomy without pedicular clamping, it makes easy the transparenchymal approach of the large vascular and biliary structures, and it is useful in hydatic cyst surgery. Although the U.S.D. is not indispensable to carry out hepatectomy, it improves intraparenchymal control of vessels and biliary ducts, making therefore hepatic resection easier.