The first 21 cases recorded in the Registry for Endometrial Carcinoma in Young Women Taking Oral Contraceptive Agents are reported. We have found no other such cases in the literature, and indeed several authors have stated that these agents, because of their predominantly progestational action, would be expected to be protective against this disease. In 8 of the 21 patients, factors were present which militated against a close relation between oral contraceptives and carcinoma, and 5 of these S patients had taken only or predominantly combined agents. On the other hand, 11 of the remaining 13 patients took sequential agents, a ratio directly opposite that of the usage of combined and sequential agents in the American population. The possible reasons for the excess of sequential agents, chiefly Oracon, arc discussed, and directions for future study are suggested.