AbstractAtypical squamous cells of undetermined significance (ASCUS) is a cytological report that creates a dilemma for the cytologist and the clinician because it does not necessarily represent a pathological entity. To clarify this paradox we propose research into the monitoring of cytological and histological results for a period of 3 years from a cohort of women treated in the Primary Care Health Services of Santiago, Chile, who have received a first Pap ASCUS results in 2005. In the cytological reports, the national nomenclature was used, which is equivalent to the Bethesda System 2001. By applying the selection criteria, a cohort of 154 women was formulated, whereby at the end of the monitoring period, we found: 2 women with invasive carcinoma (1.3%), 33 women with high‐grade squamous intraepithelial lesions HSIL (21.4%), 32 women with low grade squamous intraepithelial lesions LSIL (20.8%), and 87 women with normal results (56.5%). The statistical analysis, by form of the tree of conditional probabilities, shows that when the 2nd smear is repeated within an accelerated time frame (2.7 months), it does not assist in elucidating this cytological entity, and should be repeated only after 6 months from the first ASCUS smear result. Thus, we found that one out of every two women showed no evidence of abnormal results throughout their cytological and histological monitoring. Diagn. Cytopathol. 2011;39:258–263. © 2010 Wiley‐Liss, Inc..