Hydatidiform moles (HMs) are classified as partial or complete based on a combination of gross, histologic, and karyotypic features. Adherence to strict and reproducible diagnostic criteria is needed to ensure accurate diagnosis and minimize interpathologist variability. Using the kappa statistic as a measure of agreement, the morphologic, flow cytometric, and clinical features of 80 cases of HM or suspected HM were analyzed sequentially by three pathologists to evaluate intrapathologist and interpathologist variability. Poor interpathologist agreement was obtained when histology alone was used for diagnosis. The combination of gross morphology and histology resulted in poor to good agreement. Good interpathologist agreement was obtained, however, when objective data (DNA content determined by flow cytometry) were included in the analysis. Our data indicate that pathologist concordance is maximized when the diagnosis is based on a combination of morphology and DNA content.