This article, prepared by the medical consultant to the International Planned Parenthood Federation, reviews recent evidence regarding oral contraceptives (OCs) and cancers of the reproductive organs. Several case-control and prospective studies not only have shown that OCs do not increase the risk of cancer of the endometrium or ovary, but also that OC use exerts a protective effect against the development of these cancers. The current evidence suggests that there is no overall increase in the risk of breast cancer among OC users, but the possibility that particular groups of women (i.e., those with a history of benign breast disease or a family history of breast cancer, those who used OCs before their 1st full-term pregnancy, and women who used OCs before the age of 25 years) may be at higher risk cannot be excluded. There have been reports that breast cancer tumors have more favorable outcomes in OC users than in nonusers. Finally, the evidence that the risk of cervical cancer may be slightly increased by prolonged OC use is stronger, but not yet definitely confirmed. Most of the studies that have found an increased risk of cervical dysplasia or carcinoma of the cervix among OC users have not controlled properly for selection, diagnostic, or confounding bias. It is noted that many of the OC users included in epidemiologic studies were taking OCs marketed in the early 1960s that contained higher doses of estrogen and progestagen than preparations on the market today. Given the lack of conclusive evidence regarding the risk of cervical dysplasia and malignancy in OC users, cervical smears should be obtained on a regular basis. Despite these cautionary measures, it is concluded that OCs remain one of the most reliable methods of contraception available.