CONTEXT Knowledge of human papillomavirus (HPV) status is expected to bias the morphologic evaluation of Papanicolaou (Pap) test results. OBJECTIVE To characterize Pap test result interpretive bias when the HPV status is known at the microscopic evaluation. DESIGN Forty HPV-positive liquid-based Pap test results initially interpreted as negative for squamous intraepithelial lesion or malignancy were selected from a quality assurance program, separated into 2 groups of 20 slides each, and circulated in 2 groups to 22 members of the College of American Pathologists Cytopathology Committee. Each member reviewed each case and indicated whether the result was negative for squamous intraepithelial lesion or malignancy or was an epithelial cell abnormality (ECA). The participants assessed the severity of ECAs using the Bethesda System. The participants were not informed of the HPV status in the initial review round. Each group of 20 slides was then distributed to the opposite group (to avoid slide recall), and the participants were informed that all slides were from patients who were high-risk HPV positive. Differences in the responses between groups were analyzed by χ(2) test and Cochran-Mantel-Haenszel test at the .05 significance level. RESULTS Without knowledge of the HPV status, slides were more often categorized as negative for squamous intraepithelial lesion or malignancy and less likely identified as an ECA (P < .001). There was an increase across all categories of ECAs in the biased responses compared with the unbiased responses (P = .002). CONCLUSIONS Knowledge of positive HPV status biases morphologic Pap test result interpretation. If the HPV status is positive, observers are more likely to report a Pap test result as abnormal across all categories of ECAs.