Discrimination between complete moles (CMs), partial moles (PMs), and hydropic abortions (HAs) is important as the risk of persistent gestational trophoblastic disease (GTD) differs for each condition. We evaluated whether ancillary fluorescence in situ hybridization (FISH) with a set of chromosome enumeration probes (CEP) for chromosomes X, Y, and 17 and p57 immunostaining could improve the clinical diagnosis. Forty-one products of conception (POC) were reclassified according to clinical performance, morphology, p57 immunostaining results, and FISH results. The accuracy of histological examination alone was 85% for the original diagnosis. FISH analysis showed diploidy in 19 of 20 CMs and triploidy in 4 of 6 PMs. The concordance rate was 92.5% on using the CEP probes. p57 Staining was negative in all CMs and positive in all PMs and HAs. Chromosomal abnormality was detected in 3 cases of HA by using FISH. In conclusion, combined p57 immunostaining and FISH with a set of 3 CEP probes for chromosomes X, Y, and 17 could be useful in the classification of hydatidiform moles. (C) 2014 Elsevier Inc. All rights reserved.