The Bethesda System recommends that the diagnosis of "atypical squamous cells of undetermined significance" (ASCUS) be qualified when possible to indicate whether a reactive process, or a squamous intraepithelial lesion (SIL), is favored. In order to evaluate the utility of this recommendation, 308 cervicovaginal smears diagnosed as ASCUS favoring a reactive (FR) or dysplastic (FD) process were identified. Concurrent or follow-up biopsies and cervicovaginal smear results were reviewed and compared to the follow-up of 103 cervicovaginal smears diagnosed as ASCUS without qualification. A follow-up diagnosis of SIL was found in 46.5%, 29.5% and 26.2% of the ASCUS FD, ASCUS FR, and ASCUS unqualified cases, respectively. A repeated ASCUS diagnosis was found in 20.4%, 21.8%, and 18.4% of the ASCUS FD, ASCUS FR, and ASCUS unqualified cases, respectively. Follow-up of each group was negative for dysplasia in 30.0%, 48.7%, and 54.4% of the ASCUS FD, ASCUS FR, and ASCUS unqualified cases, respectively. These results support the use of an ASCUS FD category for the increased detection of patients with dysplasia. The ASCUS FR category was not helpful in our laboratory. Follow-up studies of qualified ASCUS cases in individual practice settings may be useful in guiding patient management.