Despite the increasing utilization of the ThinPrep® Pap Test (TP), limited data exist regarding the cytomorphologic features and patterns of invasive squamous-cell carcinoma in TP specimens. We analyzed a series of TP specimens from patients with histologically confirmed invasive squamous carcinomas of the cervix. Patients with biopsy-proven invasive squamous-cell carcinoma of the cervix with a TP cervical cytologic specimen within the previous 2 mo were identified. The TP slides were analyzed for overall cellularity (percent circle coverage by epithelial cells), tumor cellularity, tumor diathesis, inflammation, coexistent dysplasia, and keratinization. Tumor cellularity was defined as <5%, 5–50%, and >50% of slide cellularity. In all 13 cases that were identified, a cytologic diagnosis of either invasive squamous-cell carcinoma or suspicious for invasive squamous-cell carcinoma was made. In 7/13 cases (54%), epithelial cells covered <40% of the slide circle. Epithelial cells covered >40% of the slide circle in 6/13 cases (46%). Tumor cellularity covered <5% of the slide circle in 4/13 cases (31%), 5–50% in 7/13 cases (54%), and >50% in 2/13 cases (15%). A tumor diathesis was present in 12/13 cases (92%). Inflammation was absent in 1/13 cases (8%), mild in 8/13 cases (62%), moderate in 2/13 cases (15%), and severe in 1/13 cases (8%). Coexistent dysplasia was identified in 12/13 cases (92%). Keratinization was identified in 9/13 specimens (69%). In the vast majority of patients, a diagnosis of squamous-cell carcinoma was rendered on the TP cervical specimen, despite a pattern of decreased cell coverage. It could be hypothesized that tumor diathesis and inflammation may be the etiology for decreased cellularity by blocking filter coverage by epithelial cells. This cellular pattern with diathesis in the ThinPrep® smear may be a useful clue to look carefully for diagnostic cells of squamous-cell carcinoma. Diagn. Cytopathol. 2002;26:1–4. © 2002 Wiley-Liss, Inc.