A total of 71 consecutive patients with unresectable hepatocellular carcinoma were analyzed retrospectively to determine the significant prognostic factors. All the patients received systemic chemotherapy in a phase 2 study from 1980 to 1990, with no other anticancer treatment. Median survival time and 1-yr and 2-yr survival rates were 5.6 mo, 23% and 5%, respectively. By the univariate analysis, a performance status of 0-1 and tumor size less than 50% of the liver cross-sectional area were shown to be the factors most significantly favoring a better prognosis. By the multivariate analysis using the Cox proportional hazards model, a performance status of 0-1 (p < 0.001), absence of tumor thrombus in the main portal trunk (p = 0.003) and age less than 60 yr (p = 0.036) were independent favorable prognostic factors. A prognostic index was calculated from these three factors according to the following equation: 1.8109 x (0 = performance status of 0-1 and 1 = performance status of 2-3) + 0.9322 x (0 = tumor thrombus absent in the main portal trunk and 1 = present) + 0.6996 x (0 = age < 60 yr and 1 = age greater-than-or-equal 60 yr). This index was used to classify the patients into three groups with a good, intermediate and poor prognosis. The median survival times for these three groups were 9.8, 3.8 and 1.9 mo, respectively (p < 0.01). The results of this study may be useful in the design and analysis of future clinical trials of systemic therapy for hepatocellular carcinoma.