The authors compared the accuracy of conventionally prepared smears and smears prepared by an automated, fluid-based, thin-layer processing device in the detection of cytologic abnormalities. A total of 3218 patients from five centers took part in this study, in which a single cervical sample was split into a matched pair. The conventional smear was made in the routine fashion; the remainder of the cells on the sampling device were rinsed into a transport-fixation fluid. A slide was then prepared from the solution using the thin-layer processor. Diagnostic findings identified on the two preparations were compared in a blinded fashion, and a discrepancy resolution procedure was used to eliminate screening differences. Overall, there was a high correlation in the diagnoses of the two methods. For low-grade or more severe disease, the thin-layer method resulted in a 13% increase in the rate of detection, as compared with the conventional Papanicolaou smear technique.