Objective: The Bethesda System (TBS) of uterine cervical cytology is a classification method that can improve accuracy in management and it includes descriptions on adequate specimens, human papillomavirus (HPV) involvement and estimated lesions. However, the judgment of atypical squamous cells of undetermined significance (ASC-US) using TBS features complicated diagnostic criteria and poor reproducibility due to the definition of ASC-US. Of patients diagnosed with ASC-US in the initial cytology, cervical intraepithelial neoplasia (CIN)1-2 cases positive for high-risk HPV (CIN+) and benign cases in histology negative for high-risk HPV (B-) were selected for discriminant analysis based on Mahalanobis distance, in order to improve the accuracy of the ASC-US diagnosis. Study Design: ASC-US cases featuring koilocytosis with little nuclear atypia (koilocytosis) and squamous epithelial cells with nuclear atypia (SC with atypia), morphologically diagnosed with liquid-based cytology specimens prepared using ThinPrep were included. The nuclei of koilocytosis cases (CIN+, 8 cases, and B-, 10 cases) and SC with atypia (CIN+, 19 cases, and B-, 15 cases) were three-dimensionally analyzed to conduct a discriminant analysis based on Mahalanobis distance. Results: Discrimination rates were 78.9% for CIN+ and 66.7% for B- in koilocytosis, and 50.7% for CIN+ and 72.1% for B- in SC with atypia. Conclusion: The present method allows the objective analysis of nuclear chromatin, providing effective cytology regarding CIN+ in koilocytosis and B- in SC with atypia of ASC-US cases.