Hepatocellular carcinoma patients were categorized into three grades according to the extent of portal vein invasion by the tumor. Correlations between the extent of portal vein invasion and values of alpha-fetoprotein (AFP), and various biochemical tests were examined. The extent of portal vein invasion by the tumor significantly correlated with the values of glutamic oxaloacetic transaminase (GOT), glutamic oxaloacetic transaminase: glutamic pyrubic transaminase (GOT:GPT), lactic dehydrogenase (LDH), alkaline phosphatase, leucinaminopeptidase (LAP), gamma-glutamic transpeptidase (gamma-GTP) and log10AFP. Results of the multivariate logistic regression analysis showed the values of LAP, LDH, log10AFP and GOT:GPT to be statistically significant independent indicators of portal vein invasion by hepatocellular carcinoma. The calculated probability for portal vein tumor thrombus, which was derived from the results of a step wise multivariate logistic regression procedure, revealed high accuracy and specificity for predictability. To design effective therapy and to predict the prognosis, it would be beneficial to obtain additional information from this calculated probability in patients with hepatocellular carcinoma.