The Japan Integrated Staging score (JIS score), which combines the Child-Turcotte-Pugh classification and tumor-node-metastasis staging, has been proposed as a better prognostic staging system for hepatocellular carcinoma (HCC) than the Cancer of the Liver Italian Program (CLIP) scoring system. In this study, validation was performed among a larger patient population. A total of 4,525 consecutive patients with HCC who had been diagnosed at five institutions were included. Stratification ability, prognostic predictive power, and reproducibility were analyzed and compared with results from the CLIP scoring system. Only 45% (1,951 of 4,525) of all patients were categorized as early stage HCC according to JIS score (0 or 1), whereas 63% (2,878 of 4,525) of the patients were categorized as having a CLIP score of 0 or 1. Significant differences in survival curves were not observed among CLIP scores 3 to 6. In contrast, survival curves showed significant differences among all the JIS scores. The same JIS scoring subgroups showed a similar prognosis, and good internal reproducibility was observed in each of the institutions. Multivariate analysis of the prognosis in all 4,525 patients proved the JIS score to be the best prognostic factor. Furthermore, the Akaike information criteria proved that the JIS scoring system was statistically a better model for predicting outcome than the CLIP scoring system. In conclusion, the stratification ability and prognostic predictive power of the JIS score were much better than that of the CLIP score and were simple to obtain and remember.