CONTEXT: The relationship between levels of contraceptive use and the incidence of induced abortion continues to provoke heated discussion, with some observers arguing that use of abortion decreases as contraceptive prevalence rises and others claiming that increased use of family planning methods causes abortion incidence to rise. METHODS: Abortion trends are examined in countries with reliable data on abortion and with contraceptive prevalence information from two points in time showing increases in contraceptive use. The role of changes in fertility in mediating the relationship between abortion and contraception is also explored. RESULTS: In seven countries--Kazakhstan, Kyrgyz Republic, Uzbekistan, Bulgaria, Turkey, Tunisia and Switzerland--abortion incidence declined as prevalence of modern contraceptive use rose. In six others--Cuba, Denmark, Netherlands, the United States, Singapore and the Republic of Korea--levels of abortion and contraceptive use rose simultaneously. In all six of these countries, however, overall levels of fertility were falling during the period studied. After fertility levels stabilized in several of the countries that had shown simultaneous rises in contraception and abortion, contraceptive use continued to increase and abortion rates fell. The most clear-cut example of this trend is the Republic of Korea. CONCLUSIONS: Rising contraceptive use results in reduced abortion incidence in settings where fertility itself is constant. The parallel rise in abortion and contraception in some countries occurred because increased contraceptive use alone was unable to meet the growing need for fertility regulation in situations where fertility was falling rapidly.