Both p16 and retinoblastoma (Rb) proteins are important tumor suppressors that regulate the cell cycle. The status of both proteins in invasive cervical cancer and cervical intraepithelial neoplasia (CIN) has not yet been examined. The aim of this study was to investigate the expression of p16 and Rb proteins by immunohistochemistry using 98 formalin-fixed and paraffin-embedded samples of various cervical neoplastic lesions. Strong immunoreactivity for the p16 protein was observed in both the nuclei and cytoplasm of all CIN and invasive cancer cases except several low-grade CIN lesions. Expression of Rb protein was also demonstrated in the scattered nuclei of neoplastic and normal cells in all cases investigated. The results suggest that the deletion or mutational inactivity of both p16 and Rb proteins may be a rare event in cervical carcinogenesis. Moreover, overexpression of the p16 protein may be a useful diagnostic marker for cervical neoplastic lesions on routine laboratory screening.