BACKGROUND: Atypical glandular cells (AGC) is a very important diagnosis in gynecological cytology. In the current study, the authors investigated the usefulness of Cellient cell blocks (CB) for characterizing AGC on Papanicolaou (Pap) tests. METHODS: A total of 148 patients with an AGC diagnosis based on Pap tests by cytotechnologists and referred to cytopathologists were studied. Among these patients, there were 68 patients with CB preparations and 80 patients with Pap tests only (TP-AGC group). Follow-up results by Pap tests or biopsies were obtained in 117 of 148 patients. The median follow-up was 13 months (range, 1 month-36 months). RESULTS: Of the 68 patients with CBs, 31 (46%) were reclassified as negative for dysplasia or low-grade intraepithelial lesion; 30 patients (44%) retained a diagnosis of AGC (CB-AGC group); and 7 patients (10%) were given specific diagnoses of high-grade intraepithelial lesion (3 patients), endocervical adenocarcinoma in situ (1 patient), and invasive adenocarcinoma (3 patients). On follow-up, the CB-AGC group was found to have a significantly lower rate of negative=low-grade squamous intraepithelial lesion diagnoses compared with the TP-AGC group (55% vs 85%; P 5.006). The CB-AGC group had a significantly higher rate of endocervical or endometrial adenocarcinoma compared with the TP-AGC group (36% vs 8%; P 5.003) at the time of follow-up. The rates of high-grade squamous intraepithelial lesion were not found to be statistically different between these 2 groups (9% vs 7%; P 5.66). CONCLUSIONS: The Cellient CB is a useful technique to further categorize a diagnosis of AGC on Pap tests. Using the Cellient CB system, the pathologist has the ability to improve the diagnostic accuracy of AGC so that unnecessary colposcopic evaluation or biopsies can be avoided. Cancer (Cancer Cytopathol) 2014;122:8-14. V C 2013 American Cancer Society.