Chorionepithelioma, because of its diverse and often misleading clinical and pathologic manifestations, is without doubt one of the most puzzling gynecologic conditions to prognosticate. This is the fact particularly because even expert pathologic diagnosis does not foretell the subsequent clinical course; tumors appearing relatively benign frequently run a rapidly fatal course, while tumors appearing virulently malignant may occur in patients making uneventful, complete recoveries. Much has been added in recent years to knowledge of the source, clinical course, and treatment of chorionepithelioma. When the condition was first described, its true origin was unknown. Saenger,1in 1888, believed it to arise from decidual cells and therefore he employed the term "deciduoma malignum" or "sarcoma deciduocellulare." Marchand,2in 1898, was the first to discover the true origin of the tumor cells from the fetal villi, and he demonstrated the similarity of the cells to the syncytium and Langhans' cells. He