Many genes participate in the regulation of cell cycle progression from G1 to S phase. Functional loss of one or more of these genes has been reported to be associated with carcinogenesis and/or tumor progression and poor prognosis in many cancers. In a series of 126 patients with hepatocellular carcinoma (HCC), we immunohistochemically evaluated tumor expression of the cell cycle-related gene protein products of Rb, p21 (WAF1), and p53. Positive immunostaining for Rb, p21, and mutant p53 protein was detected in 58%, 33%, and 37% of the tumors, respectively. The proportion of HCCs exhibiting aberrant p53 protein expression increased significantly with advancing stage of disease (p < 0.001), poorer histological classification of differentiation (p < 0.01), and increasing tumor size (p < 0.01). A decrease in the proportion of HCCs expressing p21 protein was also associated with advancing clinical stage of disease (p < 0.01), and larger tumor size (p < 0.05). The only clinicopathological feature found to be associated with Rb status, was intrahepatic metastasis, which occurred with a higher frequency in HCCs exhibiting positive immunoreactivity for Rb protein expression (p < 0.05). Multivariate survival analysis revealed that, amongst the protein products of the different genes evaluated, only positive immunostaining for aberrant p53 protein expression served as an independent prognostic indicator, being significantly associated with worse survival in patients with HCC (p = 0.023). Analysis for relationships between gene products showed an inverse correlation between expression of aberrant p53 protein and p21 protein (p < 0.01), and also an inverse correlation between p21 protein and Rb protein expression (p < 0.05) in these cases of HCC. These findings demonstrate that positive immunostaining for mutant p53 protein expression is a significant indicator of tumor progression and poor prognosis, confirm that p21 protein expression is induced in a p53-dependent manner, and suggest that Rb protein expression may be regulated to some extent by p21 in HCC.