An overview of the available epidemiological evidence on the connection between oral contraceptives and cancer or vascular disease is presented, including the observation that epidemiological studies have produced important indications for changing both the composition and prescription patterns of oral contraceptives to avoid a large proportion of vascular side effects. Further, the evidence is remarkably clear and consistent in relation to the elevated risks of cervical neoplasms and, although based on a limited number of small studies, of primary liver cancer; protection against endometrial and ovarian cancers up to middle age; and the absence of association with malignant melanoma. There are still uncertainties regarding breast cancer, mainly related to the role of time factors, and the potential persisting risk related to long term use at younger age: published studies, in fact, show elevated risks for long term use in women below age 35 or perhaps up to age 45, but no evidence of association in middle age. Since breast cancer and ovarian cancer account for most of the mortality burden in women up to age 50 or 55 in developed countries, a clarification of the risk relationship for these 2 neoplasms will determine most of the quantitative evaluation on positive or adverse effects of oral contraceptives. The impact of other neoplasms and of cardiovascular disease, on the basis of current oral contraceptive composition, is comparatively limited, if not negligible.