Objective To evaluate the expression and clinical significance of human papillomavirus(HPV)L1 caspid protein in cytologic specimens of the cervix.Methods The HPV L1 caspid protein in cytologic specimens of the cervix was detected by using immunochemistry in 309 women treated in Shenzhen Hospital of Peking University from Jan.2008 to May 2009.According to histological biopsy,of 309 liquid-based cytologic smears,there were 33 cases of normal cervixes or chronic cervititis,168 cases of grade I of cervical intraepithelial neoplasia(CIN I),84 cases of grade Ⅱ/Ⅲof CIN,and 24 cases of squamous cell carcinomas(SCC).Results The positive expression rate of HPV L1 caspid protein was 27.3%,66.7%,25.0%,and 0 in the normal cervixes or chronic cervititis,CIN I and CIN Ⅱ/Ⅲ,and SCC respectively.There was significant difference between CIN I or SCC and the normal cervixes or chronic cervititis,between CIN I with CIN Ⅱ/Ⅲ,and between CIN I or CIN Ⅱ/m with SCC(all P<0.0 1).The positive expression rate of HPV L1 caspid protein was reduced with the lesion progression from CIN I to CINⅡ/Ⅲ to SCC.309 cases were divided into two groups by 30 and 40 years of age,and there was no significant difference in the HPV L1 caspid protein expression between different age groups(P>0.05).The positive expression rate of HPV L1 caspid protein in the over-1000 RLU/PC viral load group was significantly higher than in the under-1000 RLU/PC viral load group(P<0.05).The sensitivity,specificity,positive predictive value,negative predictive value of HPV L1 caspid protein for detecting high-grade cervical lesions were 80.6%,60.2%,52.1% and 85.2%,respectively.Conclusion The positive rate of HPV L1 caspid protein is decreased with the lesion progression from CIN I to CIN Ⅱ/Ⅲto SCC.HPV L1 caspid protein among HPV-positive women can be a helpful molecular biomarker in risk assessment and prognostic prediction.