To examine prospectively the risk for mortality among women who had ever used oral contraceptives compared with those who had never used oral contraceptives. Prospective cohort study. Nurses' Health Study. 166,755 women aged 30 to 55 years in 1976, followed through 1988 (1.3 million person-years of follow-up). On the basis of 2879 deaths, we found no overall difference in mortality among women who had ever used oral contraceptives compared with women who had never used oral contraceptives; the relative risk for ever-users, adjusted for age, body mass index, and cigarette smoking was 0.93 (95% CI, 0.85 to 1.01). We observed no trend in risk for total mortality with increasing duration of past use of oral contraceptives. After adjusting for age, body mass index, and cigarette smoking, women who had used oral contraceptives for 10 or more years had a relative risk of 1.06 (CI, 0.83 to 1.35). Use of oral contraceptives is safe; no evidence from this study indicates that long durations of oral contraceptive use adversely affect long-term risk for mortality.