Objective To investigate using detection of human papillomavirus (HPV) L1 capsid protein to predict the COWS e of mild or moderate cervical intraepithelial neoplasia (CIN). Study Design Immunocytochemical analysis using antibody against HPV L1 capsid protein was carried out on 274 Pap tests from women positive for high-risk HPV detected by hybrid capture, with cytologic diagnoses of atypical spumous cells of undetermined significance (ASCUS), low-grade wantons intraepithelial lesion (LSIL), atypical squamous cell cannot exclude high-grade squamous intraepithelial lesion (HSIL) (ASC-H), HSIL and squamous cell carcinoma (SCC). Histologic diagnosis was available for patients after initial cytologic diagnosis. Results L1 capsid protein was positive in 69.79% of cervicitis, 83.53% of CIN 1, 41.81% of CIN 2, 3.13% of CIN 3 and 0% of SCC Cytologic diagnosis revealed a higher expression rate in LSIL than in ASCUS and HSIL + SCC. In 71 ASCUS/LSIL without treatment, no L1-positive cases progressed in cytology; 18.75% of L1-negative cases progressed to ASC-H/HSIL. Conclusion The decreased expression of HPV L1 may correlate with progressed cytopathology. The expressions of HPV L1 in liquid-based cell specimens implied the histopathology diagnoses of cervix. Expression of HPV L1 may have significance en treating ASCUS and LSIL (Acta Cytol 2010; 54:661-667)