Ultrasonographic examination of the liver segment I, based on limiting vascular ans fissural elements, requires detailed knowledge of hepatic anatomical and organizational features. Findings are of two-fold interest for pre-operative assessment. Firstly, as a complement to essential arteriography it can establish the integrity of the segment when considering hepatectomy for liver tumors, and secondly it enables application of modifications in techniques for portocaval anastomoses. The data obtained can also assist diagnosis in cases of cirrhosis and Budd-Chiaris syndrome.