The combined application of DNA cytometric and interphase cytogenetic analyses was used to find objective criteria for the differential diagnosis of complete hydatidiform mole, partial hydatidiform mole and hydropic abortion. DNA ploidy and G0/G1 exceeding rates were determined using image and flow cytometric analyses on paraffin-embedded tissues of 166 cases: 71 cases of complete mole, 20 cases of partial mole, and 75 cases of abortions. To determine the existence and histological distribution of cell subpopulations with numerical chromosome aberrations, interphase cytogenetic analysis using probes specific for chromosomes 1, X, and Y was applied to paraffin tissue sections of 23 cases: 12 cases of complete mole, 3 cases of partial mole, and 8 cases of abortions. In contrast to previously reported findings that complete moles are diploid, the results of this study showed that complete moles are DNA-polyploid (96 per cent), with high G0/G1 exceeding rates and a high frequency of numerical chromosomal aberrations in the trophoblast hyperplasia. The majority of the partial moles were DNA-triploid (55 per cent). This study, however, also showed the presence of DNA-polyploid partial moles (30 per cent). Abortions were DNA-diploid (60 per cent) or DNA-triploid (39 per cent). DNA cytometric analysis, especially image DNA cytometric analysis with determination of the G0/G1 exceeding rate, and interphase cytogenetic analysis provide objective measurements which are contributory in the differential diagnosis between complete mole, partial mole, and hydropic abortion.