We examined hepatocellular carcinomas (HCCs) that were smaller than 2 cm in diameter. Ninety-nine nodules from 65 patients were removed for treatment. The nodules were divided into four types (A, B, C and D) according to the following criteria: first, the appearance of the margin of nodules, distinct or indistinct; and second, cellular atypia, uniform or multiple as "nodules in nodule". In 45 indistinct margin nodules, 28 showed uniform atypia (type A) and 17 were of "nodules in nodule" (type B). As for 54 distinct margin nodules, 23 were "nodules in nodule" (type C) and 31 showed uniform atypia (type D). Cancer cell invasion was divided into three types: (1) stromal invasion into fibrotic tissue and/or portal tracts, (2) blood vessel wall invasion of portal veins or hepatic veins, and (3) tumor thrombus. The stromal and vessel wall invasion occurred almost at the same rate regardless of degree of atypia. This study shows that well-differentiated HCCs in which the cancer cells show only very slight atypia have the potential for metastasis to intrahepatic and other sites.