This study was undertaken to determine the effectiveness of the Papanicolaou (Pap) smear, colposcopicallydirectedbiopsy (CDB), and endocervical curettage (ECC) in preconization detection of adenocarcinoma in situ (AIS)of the uterine cervix. Women, whose cervical conization specimens contained adenocarcinoma in situ without anyassociated invasive lesion at Chiang Mai University Hospital between March 1998 and March 2006, were reviewed.During the study period, fifty-one women who matched the study inclusion were identified. Glandular abnormalitywas detected by Pap smears in 22 women (43.1%). Among 29 women with squamous lesions on Pap smears, 9additional glandular abnormalities were detected on CDB and/or ECC. In total, glandular abnormality was suspectedin 31 women (60.8%) preoperatively. According to the histological type of AIS, glandular abnormality suspectedfrom preoperative evaluation was noted in 20 women (70.4%) who had pure AIS. Among women with mixed AIS/HSIL, only 12 women (50.0%) had preoperative evaluation suggesting glandular abnormality. These data demonstratethat the sensitivity of combining Pap smear, CDB and/or ECC in detecting glandular lesions before conizationcontaining AIS appears to be suboptimal. Further study concerning the improvement of detecting AIS before conizationis warranted to select the most appropriate diagnostic conization method for such lesions.