The nuclear DNA contents in fresh surgical specimens in cases of 34 hepatocellular carcinoma were measured by flow cytometry. The frequency of aneuploid and relation of ploidy with degree of malignancy (stage and portal vein thrombosis, etc.) were examined. The incidence of aneuploidy of human hepatocellular carcinoma was 53%, these cases were at a significantly higher stage than the diploid cases (P less than 0.05). Among aneuploid cases, 61% (11 out of 18 cases) were associated portal vein thrombosis, this incidence was also significantly higher than the 6% (one of 16 cases) for the diploid cases (P less than 0.01). These findings demonstrated flow cytometric analysis are not only useful to diagnose to hepatocellular carcinoma, but useful to evaluate the prognosis.