OBJECTIVE To detect the proliferative activity of cervical cells in cervical intraepithelial neoplasia (CIN) and cervical carcinoma by using proliferating cell nuclear antigen (PCNA) immunohistochemistry and mitotic index (MI). METHODS Sixty specimens of CIN and cervical carcinoma from patients treated at the Obstetrics and Gynaecology Hospital, Shanghai Medical University, were analyzed. Among them, 8 were CIN I-II, 16 CIN III, 18 squamous carcinoma, and 18 adenocarcinoma. Serial 4 microns sections were prepared for haematoxylin and eosin (HE) staining to observe mitotic figure and pathological grading and for immunohistochemical staining of PACN which was performed by murine monoclonal antibody PC 10 (DAKO-PCNA). RESULTS PCNA index (PI) and MI of CIN III and cervical carcinoma were significantly higher than those of normal cervix and CIN I-II. PI and MI increased with progress of disease. In addition, higher level of PI was correlated with higher level of MI, and higher levels of PI and MI were related with higher histological grade. However, there was no significant relationship between PI, MI, clinical staging, and lymph node metastases. CONCLUSION PCNA and mitotic figure are useful for evaluating proliferative activity in CIN and cervical carcinoma, and could be used to distinguish CIN III from CIN I-II and evaluate the malignant potential of tumour tissues.