Objective : To estimate false-negative rate of cervical smears in histologically confirmed squamous intraepithelial lesion and squamous cell carcinoma. Method : From 1993 to 1998, total 186 cases of cervical smear performed within 1 year before histological confirmation squamous intraepithelial lesion and squamous cell carcinoma, were reviewed and the false negative rate of the each group was analyzed. Results : 1. Histologic diagnosis of 186 cases includes 8 cases of low grade SIL, 87 cases of high grade SIL, 91 cases of squamous cell carcinoma. 2. Overall false negative rate was 18.8% (35/186). False negative rate of LSIL was higher (50%; 4/8) compared with the other two groups. (HSIL:23% ;20/87, SCC:12.1% ;11/91) 3. 18 of 35 false negative cases were reviewed. 8 cases(44.4%) were sampling error and 10 cases(55.6%) were interpretation error. 4. Estimated overall sampling error was 8-9% ; interpretation error 10-11%. Conclusion : Reducing the false negative rate of cervical smears, especially in cervical intraepithelial neoplasia lesion is important to save the patients from invasive cervical cancer. Further studies on the causes of false negatives and the efforts to eliminate these barriers are actually needed.