Hydropic placentas may be classified by histopathology into hydropic abortus, partial hydatidiform mole, and complete hydatidiform mole. We studied 142 hydropic placentas: 39% were complete hydatidiform moles, 35% partial hydatidiform moles, and 26% hydropic abortuses. Villous vesicle size was predictive of histologic diagnosis. We determined DNA ploidy in 137 cases. Seventy-three percent of hydropic abortuses were diploid and 11% were triploid. Ninety percent of partial moles were triploid or near-triploid; one partial mole was haploid and one diploid. Of the complete moles, 50% were diploid, 43% were tetraploid, 3.6% polyploid, and 1.7% triploid. Partial moles had lower pre-evacuation beta-hCG levels than complete moles. Persistent tumor followed 33% of complete moles and 12% of partial moles. Although the numbers were small, no patient with a diploid, tetraploid, aneuploid, or haploid partial mole developed persistent disease. Among complete moles, the pre-evacuation beta-hCG level was not predictive of persistence (P = .15). Subdividing complete moles by ploidy, we found that tetraploid moles were associated with higher pre-evacuation beta-hCG levels than were diploid moles. However, tetraploidy was not associated with increased persistent tumor among complete moles. Although most partial moles were triploid and most complete moles were diploid or tetraploid, there was wider DNA heterogeneity among molar gestations than previously reported. In this series, DNA ploidy was not an independent predictor of persistence in complete moles.