To determine the cytologic and histologic correlation of atypical glandular cells of undetermined significance (AGUS) in Papanicolaou smears, a cytology file from January 1998 to May 1999 was reviewed. Surgical pathology files were searched to determine which patients received subsequent biopsies. One hundred thirty-two patients with AGUS were identified. Corresponding biopsies were available for 82 of these cases. AGUS has been sub-classified into 3 subtypes: 1) AGUS, favor reactive; 2) AGUS, not otherwise specified; and 3) AGUS, favor neoplasia. The pathologic findings for the respective Papanicolaou smears with the diagnosis of each subtype of AGUS through the follow-up period were as follows: benign lesions in 56.1%, 0%, and 1.2%; squamous intraepithelial lesions 2.4%, 0%, and 1.2%; glandular intraepithelial lesions 0%, 0%, and 17.1%; endometrial simple hyperplasia 1.2%, 0%, and 0%; and carcinoma 0%, 9.8%, and 11%, respectively. In conclusion, AGUS, on cervical cytologic screening, was correlated with significant pathologic findings in 41.5% of the patients (37.8% with preinvasive or invasive glandular lesions and 9.6% with combined squamous intraepithelial lesions). It is thought that intensive follow-up studies, including colposcopy, cervical biopsy, and curettage, should be recommended for complete evaluation of AGUS.