The 2001 Bethesda System for reporting cervical or vaginal cytologic diagnoses is an incremental change in the uniform terminology introduced in 1988 and revised in 1991. The 2001 Bethesda System includes specific statements about specimen adequacy, general categorization, and interpretation and results. In the adequacy category, "satisfactory" and "unsatisfactory" are retained, but "satisfactory but limited by" is eliminated. The new category of "atypical squamous cells" (ASC) replaces the category of "atypical squamous cells of undetermined significance" (ASCUS) and is divided into qualifiers of (1) ASC of "undetermined significance" (ASC-US) and (2) "cannot exclude high-grade squamous intraepithelial lesion (HSIL)," or (ASC-H). The categories of ASCUS, "favor reactive" and "favor neoplasia" are eliminated. The terminology for low-grade squamous intraepithelial lesions (LSILs) and HSILs remains unchanged. The category of "atypical glandular cells of undetermined significance" (AGUS) is eliminated to avoid confusion with ASCUS and is replaced by the term "atypical glandular cells" (AGC), with attempts to identify whether the origin of the cells is endometrial, endocervical, or unqualified. "Endocervical adenocarcinoma in situ" and "AGC, favor neoplastic" are included as separate AGC categories. The presence of normal or abnormal endometrial cells is to be reported in women who are at least 40 years of age. Educational notes and comments on ancillary testing may be added as appropriate.