Background: ASC-US cases are managed according to the current American Society for Colposcopy and Cervical Pathology (ASCCP) guideline in which a human papillomavirus (HPV) test and repeat Pap smear are performed in the next 1 year. Colposcopy in cases of positive high risk HPV and persistent ASC-US or more in subsequent Pap smear is recommended. The HPV test is more expensive and still not currently a routine practice in Thailand. Objective: To identify the risk factors of persisted abnormal Pap smear and the colposcopic requirement rate in women with ASC-US. Materials and Methods: During 2008-2013, this study was conducted in Prapokklao Hospital, Chanthaburi, Thailand. Participants were women who attended gynaecology clinic for cervical cancer screening. Women who had cytological reports with ASC-US were recruited. During the study period, 503 cases were enrolled. Colposcopic requirement was defined as those who were detected with an ASC-US or more in subsequent Pap smears up to 1 year follow-up. Results: The colposcopic referral rate was 23.2 (85/365) percent at 12 months. Prevalence of cervical intraepithelial neoplasia (CIN) 2/3 was 3.3 (12/365) percent. Loss follow-up rate of subsequent Pap smear and colposcopic appointment were 27.4 (138/503) and 48.2 (41/85) percent, respectively. There was no invasive cancer. High risk factors for persisted abnormal Pap smears in subsequent test were premenopausal status, HIV infected patients and non-oral contraceptive pills (COC) users. Conclusions: Referral rate for colposcopy in women with ASC-US reports was rather high. Loss to follow-up rate was the major limitation. Immediate colposcopy should be offered for women who had high risk for silent CIN.