Objectives: To evaluate the frequency of cytohistologic discrepancy of high-grade squamous intraepithelial lesions (HSILs) in Pap smears and associated factors. Methods: Medical records of 223 women with HSIL Pap smears who were treated at Thammasat University Hospital were reviewed. Data on age, parity, menopausal status, contraceptive use and colposcopic directed biopsy and loop electrosurgical excision procedure (LEEP) pathology results were recorded. Results: Mean (SD) age of patients was 38.0 (9.4) years. The majority were premenopausal (86.5%) and multiparous (83.9%). Cytohistologic discrepancy between the Pap test and colposcopic-directed biopsy histology was 45.7% and that between the Pap test and LEEP histology was 29.5%. Fifty-four (24.2%) women had no high-grade CIN on both colposcopic directed biopsy and LEEP. Nulliparity, postmenopausal status and having no oral contraceptive pills use were factors associated with cytohistologic discrepancy. Conclusion: The exact cytohistologic discrepancy rate was relatively high (24.2%). Factors associated with cytohistologic discrepancy were nulliparity and postmenopausal status and having no oral contraceptive pill use.