In applying the Bethesda System of classification to cervical squamous lesions, we evaluated the Papanicolaou smears, cervical biopsies, and human papillomavirus (HPV) DNA status of 76 clinic patients. The biopsy specimens and concurrent Papanicolaou smears were analyzed using criteria for low-grade and high-grade squamous intraepithelial lesions, and the biopsies were analyzed for HPV DNA by in situ hybridization. Two independent observers produced good agreement in both cytologic (kappa = 0.62) and histologic (kappa = 0.71) diagnoses. Predictive values of high-grade cytology (for high-grade histology) were high (0.95 for reviewer 1; 0.97 for reviewer 2), and both high-grade cytology and histology correlated strongly with certain "high-risk" HPV types. In contrast, the predictive value of low-grade cytology for either low-grade histology or HPV types other than "high risk" was poor. This study supports the use of certain histologic criteria for distinguishing squamous intraepithelial lesions into two grades. Limitations in cytologic-histologic correlation appear to reflect the absence of cytologic criteria for distinguishing well-differentiated precursor lesions associated with high-risk HPV types.