Of the malignant tumors occurring in the male, chorionepithelioma is considered to be rare. Some 200 cases have been recorded thus far in the entire literature. Its mode of origin is still uncertain, and many theories have been advanced to explain its presence in the male. These theories have recently been reviewed in a critical survey by Mathieu and Robertson.1 Most authors accept the hypothesis advanced by Schlagenhaufer,2 that chorionepithelioma arises in a teratoma in which some structure having the morphologic value of an included ovum had differentiated into trophoblastic epithelium. Theoretically, teratomas may occur anywhere in the body, and they have been described in such areas as the mediastinum, the abdomen, the jaw and the sacrum. If chorionepitheliomas are to be considered as developing from teratomas, they need not always arise in the testes, although the tumors usually are found in these organs. The existence in the