Percutaneous transhepatic portography was performed in 31 patients. Based on the anterior and lateral images, the authors have concluded that the portal vascular system described in most anatomy textbooks does not correspond to the anterior portogram. A more practical nomenclature and order of branches are proposed, in which the first order includes the proximal portal vein branches; the second order includes the right anterior and posterior segmental branches, the umbilical portion of the left lobe, and most of the caudate veins; and the third order includes the peripheral (subsegmental) branches. The liver is divided accordingly into three main segments and one secondary segment (the caudate lobe), with each of the main segments being divided into two subsegments. The authors suggest that this new nomenclature will be helpful in both diagnosis and surgery.