This study was undertaken to evaluate the incidence and independent predictors of unexpected invasivecancer of cervix in women with high-grade squamous intraepithelial lesions (HSIL) on Pap smear who hadundergone “see and treat” approach. Women with HSIL on cervical cytology undergoing colposcopy, followedby loop electrosurgical excision procedure (LEEP) at Chiang Mai University Hospital between January 2001and April 2006 were analyzed. During the study period, 446 women were identified. Mean age was 45.6 years(range, 25-78 years). One hundred and twenty-one (27.1%) women were postmenopausal. Unsatisfactorycolposcopy was observed in 357 (80.0%) women. Of the 446 women, 76 (17.04%, 95% CI= 13.67 to 20.86) hadinvasive lesions on LEEP specimens. Multivariate analysis revealed that unsatisfactory colposcopy andpremenopausal status were statistically significant independent predictors for invasive lesion on “see and treat”LEEP with an adjusted odds ratio of 4.68 (95%CI=1.82 to 12.03, P< 0.01) and 2.10 (95%CI=1.12 to 3.94, P=0.02),respectively. In conclusion, occult invasive lesion of the cervix was noted in 17% of women with HSIL Papsmear who underwent “see and treat” approach at our institute. Unsatisfactory colposcopy and premenopausalstatus were significant independent predictors of having such lesion.