We studied branching of the intrahepatic portal vein and hepatic segment by percutaneous transhepatic portograms in 237 patients with liver, biliary tract, or pancreatic disease. At the hilum, the pattern was normal in 74% of the patients. In the others, branching of the right posterior branch was trifurcated or independent. Caudate branches usually ramified from first-order branches, but sometimes ramified from the right posterior branch. The left portal branch divided into a laterodorsal branch (second-order) and umbilical portion, from which the lateroventral branch (third-order) and several medial branches (fourth-order) arose. It seems to be better to divide the left lobe into anterior segment (supplied by medial and a lateroventral branch) and posterior segments (supplied by a laterodorsal branch) than into the lateral and medial segments. The right anterior branch of 27% of the patients was bifurcated. In the others, there were six other patterns, with four or five fourth-order branches arising from this branch. The anterior segment should be considered having not two subsegments, but four or five small subsegments. Small branches divided off from the main trunk of the right posterior branch. In resection for hepatoma, each such branch can be thought of as one small subsegmental branch.