The Thin Prep Pap Test (Cytyc Corp., Boxborough, MA) received approval by the Food and Drug Administration in May 1996 as an alternative to the traditional conventional smear. The present direct-to-vial study assessed the utility of thin-layer technology for cervicovaginal screening in clinical practice. From May 1997-February 1998 (10 mo), 15,006 cervical smears were processed and evaluated; of these, 5,423 (36.1%) were conventional smears (CS) and 9,583 (63.9%) were Thin Prep slides (TP). Both methods were analyzed to compare specimen adequacy and detection rates of cervical lesions. The TP method reduced the "satisfactory but limited by" rate by 97% and the unsatisfactory rate by 63%. For low-grade squamous intraepithelial lesions (LSILs), TP slides yielded 3.6% (348/9,583) as compared to 0.98% (53/5,423) for CS, an increase of 267%. The TP method detected a threefold increase in the number of high-grade squamous intraepithelial lesions (HSILs) of 1.0% (100/9,583), as compared to 0.3% (17/5,425) for the CS group. The atypical squamous cells of undetermined significance/squamous intraepithelial lesion (ASCUS SIL) ratio was reduced by 54% in the TP group. In routine usage in our laboratory, the Thin Prep Pap Test yielded a significant increase in the detection of LSILs and HSILs as compared to conventional smears. Specimen adequacy was significantly improved.