The extended use-effectiveness of IUD and oral pills as measured by 1) their theoretical effectiveness 2) consistency of use and 3) continuation of use in preventing unwanted pregnancies was studied for 2900 women who had chosen either method as their first contraceptive in family planning clinics in Atlanta Georgia and in Brooklyn and Buffalo New York for a 12-18 month period. The greater persistence among IUD users to continue the method or use another method and the less likelihood there was of these women to have an unplanned pregnancy (the difference between IUD users and pill users increasing with months of exposure) suggest the necessity of greater support from the clinics to help women using pills prevent unwanted pregnancies. IUD users were generally older than pill acceptors and among IUD contraceptors the greater tendency to continue using the IUD and contraception may indicate that older women use contraception to terminate rather than to space childbirth.