Objectives.The aim of this study was to evaluate the efficacy of the follow-up methods and results of atypical glandular cells of undetermined significance (AGUS) detected on cervicovaginal Pap smears.Methods.From May 1991 to December 1996, we have performed 407, 451 cervicovaginal Pap smears, of which 326 patients were identified as AGUS. Of the 326 patients, 268 patients were followed by repeat Pap smears, colposcopy, cone biopsy, or endometrial curettage.Results.The incidence of AGUS on Pap smears is approximately 0.08%. The mean age of the patients was 43 years (range 22–79 years). The most common complaint was abnormal vaginal bleeding. The gross findings of the cervix were normal to mild erosion. The following past histories of patients could affect the AGUS results on Pap smear: 30 had cone biopsy, 21 had Pap smears on pregnancy and within 8 weeks after delivery or evacuation, 3 were on hormonal replacement therapy, 2 had intrauterine devices for contraception, and 5 were undergoing follow-up after treatment of cervical cancer. The benign lesions detected during follow-up periods were 6 microglandular hyperplasia of the cervix, 5 atypical squamous metaplasia of the cervix, 2 cervical endometriosis, 2 tubal metaplasia, 10 cervical myoma, 11 cervical polyps, 9 endometrial polyps, 3 uterine myoma, 1 pelvic endometriosis, 1 ovarian endometriosis, and 4 uterine adenomyosis. The premalignant or malignant lesions of the cervix were 4 low-grade squamous intraepithelial lesions, 24 high-grade squamous intraepithelial lesions, 8 glandular atypia/dysplasia, 5 adenocarcinomain situ,3 microinvasive adenocarcinoma, and 4 invasive adenocarcinoma. The neoplastic lesions of the uterus were 6 endometrial hyperplasia, 11 endometrial adenocarcinoma, 1 malignant mixed Müllerian tumor, and 1 metastatic endometrial adenocarcinoma. Sixty-seven (25%) of 268 patients followed up were identified as having clinically significant lesions of the cervix or uterus. The detection rates of abnormal lesions were 3.1% with repeated Pap smears (3/98), 28.4% with colposcopic-directed biopsy (31/109), 63.6% with cone biopsy (35/55), and 29.7% with endometrial curettage (19/64).Conclusion.AGUS on Pap smears showed various benign and malignant lesions of the cervix or uterus. The clinicians must communicate with the pathologists regarding the patient's clinical information as well as the origin of the atypical glandular cells in Pap smears. We recommend that patients with AGUS on Pap smear should undergo immediate intensive diagnostic studies, including colposcopic-directed biopsy with endocervical curettage or cone biopsy, to detect cervical lesions and endometrial curettage to detect endometrial lesions.