We studied the pattern of intrahepatic micrometastases using large pathologic sections on liver resection specimens with ample resection margins from 113 patients with a solitary hepatocellular carcinoma (HCC). The liver tissues around the HCC were divided into proximal and distal areas according to the direction of the portal vein flow. These areas were further divided into zones based on fixed criteria. Altogether, 273 micrometastases were identified, including 254 (93.0%) intravascular micrometastases and 19 (7.0%) tumor satellite micronodules. The distance of spread of these micrometastases ranged from 0.05 to 6.10 cm. The number of micrometastases was less in the proximal area than in the distal area. In addition, the farther the distance away from the primary tumor, the fewer micrometastases there were. Micrometastases extended beyond the 2 cm margin in only nine (8.0%) patients. In conclusion, micrometastases could spread via invasion of portal vein branches at an early stage even when the tumor was solitary and small. Anatomic segment resection is preferred for patients with a solitary HCC. Nonanatomic resection may be used as an alternative in patients with impaired liver function, but adequate resection margins should be achieved. For HCCs < or = 3 cm, a proximal resection margin and a distal margin of 1.0 cm are recommended. For HCCs > 3 cm, a 1.0 proximal resection margin and a 2.0 cm distal margin are recommended.