Because oral contraceptives are used by tens of millions of healthy women, their safety for short-term and long-term use is an important issue that has been examined in a large number of epidemiologic studies. These studies have become more rigorous and have increased in size and analytic sophistication over the years. Although breast cancer remains the most important safety concern, the bulk of recent data suggests that oral contraceptives have no overall impact on a woman's risk of developing this disease. The results are less clear on the risk of cervical cancer and its precursors because of methodologic problems. However, the newer oral contraceptive formulations no longer appear to be associated with an increased risk of myocardial infarction or stroke.