The purpose of this study was to apply atypical squamous cells of undetermined significance (ASCUS) criteria from the Bethesda System for Reporting Cervical/Vaginal Cytologic Diagnoses (TBS) to the rescreen of cases previously diagnosed as ASCUS, to compare initial and rescreen diagnoses, and to analyze agreement with follow-up (cytology or histology). Two cytotechnologists (S.B. and M.J.M.) and one cytopathology fellow (M.A.) rescreened 632 cervicovaginal specimens diagnosed as ASCUS between June 1, 1992–December 31, 1995. Age and LMP were provided. Rescreen diagnoses were categorized as within normal limits (WNL), ASCUS, low-grade squamous intraepithelial lesions (LSIL), high-grade squamous intraepithelial lesions (HSIL), or carcinoma (CA). Complete agreement was found in 200 specimens (32%): 31 (15%) WNL; 91 (45%) ASCUS; 77 (38.5%) SIL; and one (0.50%) CA. Follow-up revealed no abnormality in 67% of the cases reclassified as WNL, 49% of the cases reclassified as ASCUS, and 48% of the cases reclassified as squamous intraepithelial lesions (SIL). SIL was found in 29% of cases reclassified as WNL, 29% of specimens rediagnosed as ASCUS, and 34% of cases reclassified as SIL. Partial agreement was found in 391 specimens (62%). In 41 specimens (6%), rescreeners were in complete disagreement, and follow-up revealed 9/41 (22%) SIL or worse; 21/41 (51%) WNL; and 4/41 (10%) inconclusive. Applying established criteria, 14% (91/632) of cases diagnosed as ASCUS resulted in complete agreement, and 30% (190/632) resulted in partial agreement. Follow-up of cases initially diagnosed as ASCUS revealed SIL or CA in 30% of cases. ASCUS is a significant diagnosis warranting careful patient follow-up. Diagn. Cytopathol. 2001;25:138–140. © 2001 Wiley-Liss, Inc.