To investigate the accuracy rates of cytology in abnormal cervical smears and the factors contributing to a discrepant diagnosis between cytology and histology repots of cervical intraepithelial and invasive neoplasm. During the four-year period 1993 to 1996, abnormal cervical smear findings, which were followed by cervical biopsy, were available in 709 patients. The cytology and histology slides were reviewed in each case. The accuracy rates of cytology before and after review were investigated. The accuracy rate of cytology was 48%. Following review it became 56%, mainly due to a reduction in the number of cases in which the smear showed a lesser degree of CIN than did the biopsy. The proportion of cases in which the cytological impression of CIN was more severe than the histology was minimally altered. The results suggest that difficulty in the interpretation of cervical smear as well as sampling errors are responsible for reduced accuracy even in smears which are considered representative of the pathological process.