Although an association between oral estrogens and endometrial cancer has been reported, at a disputed magnitude of risk, in nine case-control studies (1-9), no data are available on the relation between oral contraceptives and the subsequent occurrence of endometrial cancer. As part of a large case-control investigation of the association between estrogens and endometrial cancer (9), we have collected and analyzed data about the use of various estrogens preparations, as noted during personal interviews of all the available cases and controls. Groups were chosen with two different methods of selection for cases and controls. In the conventional method of selection,