Marked placental hydrops is generally associated with hydatidiform mole. Diagnosis of hydatidiform mole requires both villous hydrops and trophoblast hyperplasia. This report describes four cases with massive hydrops of placental stem villi without associated trophoblast hyperplasia. All four had diploid DNA content by flow cytometry. Fetal omphalocele was present in three; and one had diagnostic Beckwith-Wiedemann syndrome (BWS). In two others, there were pathologic features suggestive of BWS. The fourth fetus had multiple anomalies by ultrasound; autopsy examination of the fragmented fetus failed to disclose additional pathology. The association of massive placental hydrops involving stem villi, fetal omphalocele, and diploid DNA content is unusual. These fetal and placental findings may suggest possible BWS in some cases and allow for antenatal diagnosis of affected fetuses, clinical evaluation of additional family members, and planning for neonatal care.