The cervical smears represent the most effective technique to detect and prevent cancer of the uterine cervix, its false-negative rate is still a reason of concern among pathologists and gynecologists. This study was performed to determine the false-negative rate in cervical smears and to evaluate the causes for false negatives. The histologically confirmed consecutive 1,000 cases of Squamous Intraepithelial Lesion(SIL) and Squamous Cell Carcinoma(SCC) of the uterine cervix from the surgical files of Department of Pathology, Cheil General Hospital, from January 1992 to June 1993 were collected. All cervical smears of 1,000 cases, which obtained prior to pathologic diagnosis made, were evaluated based on cyto-histologic correlation. The false negatives were identified and cervical smears were reviewed. The reasons for false negatives were analysed as well. The results are as follows : 1. Histologic diagnoses of 1,000 cases include 252 cases of Low grade SIL(LSll.), 484 cases of Hligh grade SlL(HSIL) and 284 cases of SCC. 2. 60 cases were identified as false negatives. The false-negative rate was 6%(60/1000). Those 60 cases of false negativcs were 31 cases(51.7%) of LSIL, 23cases (38.3) of HSIL and 6 cases(10%) of SCC. 3. False-nagative rate were 12.3%6(31/252) of LSIL, 4.8%(23/484) of HSII. arid 2.1%(6/284) of SCC. 4. In 58 of 60 eases reviewed, the sampling enor were 75.9%(44/58) and screening error were 24.1%(14/58). 5. Sampling error were 65.9%(29/44) of HSIL and 2.3%(1/44) of SCC. In conclusion, the major of false negatives was sampling error and the major lesion of false negativity and sampling error was LSIL. These findings suggest that LSIL should require further investigation by colposcopy, cervicography and HPV Test in orcler tx reduced the false-negaitive rate. The supporting of sufficient clinical informations, good supervision and training of cytotechnologist, use of automated cytologic screening system in order to reduced false-negative rate in HSIL and SCC.