A multivariate analysis of data from 90 patients with unresectable hepatocellular carcinoma was performed using Cox's regression model to identify factors possibly affecting their prognoses. Thirty-one patients underwent arterial anticancer chemotherapy, and the remaining 59 patients received transcatheter arterial embolization with anticancer agents. Four of 27 variables tested for all the patients (i.e., encapsulation [p < 0.051, gross appearance of hepatocellular carcinoma [p < 0.011, clinical stage [p < 0.011 and therapy [p c 0.011) were found to be prognostically significant. Five of 27 variables tested were prognostically significant for the transcatheter arterial embolization group; they were an extension rate of hepatocellular carcinoma (p c 0.011, encapsulation (p c 0.01), a-fetoprotein (p < 0.011, prothrombin time (p < 0.01) and serum sodium (p < 0.01). Regression equations were used to describe a prognostic index. A prognostic index was defined as the regression equation derived from the results of a total of 90 patients; PI-1 = ey, where PI-1 = prognostic index 1 Y = 1.549 (gross appearance of hepatocellular carcinoma -1.344) + 0.778 (encapsulation -1.622) + 0.818 (clinical stage -1.800) + 1.760 (therapy -1.344) and prognostic index 2, the regression equation derived from the results of the transcatheter arterial embolization group of patients; PI-2 = ey, where PI-2 = prognostic index 2 Y = 1.210 (extension rate of hepatocellular carcinoma -1.576) + 1.179 (encapsulation -1.475) + 0.0001277 (a-fetoprotein -1420.792) -0.039 (prothrombin time -72.237) -0.214(serum sodium -138.427). According to the prognostic index, the patients were divided into two groups (i.e., those with the good prognoses and those with bad prognoses). According to prognostic index 1, the prognosis of the patient who did not undergo transcatheter arterial embolization therapy was 5.8 times poorer than that of the patient who underwent transcatheter arterial embolization. One-year survival rates of the former and the latter were 66% and 9.4%. respectively. According to prognostic index 2, the prognosis of the patient whose extension rate of hepatocellular carcinoma was greater than 60% of the entire liver was 38 times poorer than that of the patient