Computed tomography during arterial portography (CTAP) is acknowledge as a valuable preoperative method for the detection of small intrahepatic lesions in patients with liver neoplasm. Four patients with hepatocellular carcinoma (HCC) with marked portal extension are presented. Evaluation of intrahepatic portal blood flow was achieved more accurately by CTAP than by conventional arterial portography. CTAP also plays an important role in patients with inoperable HCC, since portal extension is the most important prognostic factor of transcatheter arterial therapy.