The endodermal sinus tumor of the ovary is a rare and highly lethal germ cell tumor. At least 10 different names have been applied to it, and so long as its name remains unsettled the collection of information will continue to be greatly impeded. One of the patients who came under our observation died after 21 months despite surgical removal of all evident disease followed by radiation and chemotherapy; the other patient, whose tumor could be removed only partially, and who received intensive chemotherapy for 4 months but refused all treatment thereafter, is well without evidence of disease 3 years after the initial diagnosis was made. Despite the dismal outlook for patients with this tumor, a few encouraging features emphasize the need to report new cases as they appear, and to continue the search for agents that will control it.