AIM: To elucidate the role of overexpressed polo-like kinase1 (PLK1) in hepatocellular carcinoma (HCC). METHODS: We prospectively collected clinicopathological, immunohistochemical and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) data from 135 HCC patients undergoing successful hepatectomy. The correlations between PLK1 mRNA expression and clinicopathologic variables were analyzed by Mann-Whitney U test. Prognostic factors were identified by univariate and multivariate analyses. RESULTS: Immunohistochemical results showed over-expression of PLK1 was mainly found in tumor tissues compared with tumor-free tissue. A similar mRNA result was obtained by semi-quantitative RT-PCR. A total of 111 samples were positive for PLK1 mRNA expression. The positive expression was correlated with venous invasion, tumor nodules and Edmondson grade. Furthermore, 1, 3, 5-year survival rates in the positive expression group were significantly lower than the negative control group. Multivariate analysis showed that positive PLK1 expres-sion was an independent risk factor for HCC. CONCLUSION: PLK1 could be a potential biomarker for diagnosis and therapy for HCC. AIM: To elucidate the role of overexpressed polo-like kinase 1 (PLK1) in hepatocellular carcinoma (HCC). METHODS: We prospectively collected clinicopathological, immunohistochemical and semi-quantitative reverse transcription- polymerase chain reaction (RT- PCR) data from 135 HCC patients undergoing successful hepatectomy. The correlations between PLK1 mRNA expression and clinicopathologic variables were analyzed by Mann-Whitney U test. Prognostic factors were identified by univariate and multivariate analyzes. RESULTS: Immunohistochemical results showed over-expression of PLK1 was mainly found in tumor tissues compared with A total of 111 samples were positive for PLK1 mRNA expression. The positive expression was correlated with venous invasion, tumor nodules and Edmondson grade. Furthermore, 1, 3, 5-year survival rates in the positive expression group were significantly lower than the negative control gro up. Multivariate analysis showed that positive PLK1 expres-sion was an independent risk factor for HCC. CONCLUSION: PLK1 could be a potential biomarker for diagnosis and therapy for HCC.