Since the introduction of oral contraceptives, their use has been associated with an increased risk of both venous and arterial thrombosis. Pulmonary embolism, myocardial infarction, and stroke are serious disorders with a considerable risk of mortality. Because worldwide over 100 million women use oral contraceptives, issues of drug safety are of great importance. The risk of venous thrombosis during low-dose oral contraceptive use is three- to sixfold increased compared with that of nonusers. The association is not only attributed to the estrogen component of the pill: the risk is twice as high for desogestrel and gestodene (third generation) containing oral contraceptives as for levonorgestrel (second generation) containing oral contraceptives. The risk of venous thrombosis is highest in the first year of use and in women with genetic or acquired risk factors for thrombosis. Both venous or arterial thrombosis are unrelated to duration of use or past use of combined oral contraceptives. The risk of myocardial infarction and stroke during low-dose oral contraceptive use is two- to fivefold increased relative to that of nonusers. The risk of arterial thrombosis induced by oral contraceptive use is more pronounced in smokers and women with hypertension, diabetes, and hypercholesterolemia. All types of thrombosis have strongly age-dependent incidences, and therefore in absolute figures the risks and effects of risk factors increase with age. The lowering of the estrogen dose in combined oral contraceptives from 50 microg to 20-30 microg in the last decade did not clearly reduce the risk of venous thrombosis, myocardial infarction, stroke, or peripheral arterial disease. For stroke and peripheral arterial disease no difference in risk was found between second and third generation oral contraceptives. For myocardial infarction study results are conflicting, and a small benefit of third- over second-generation oral contraceptives cannot be ruled out. However, this is unlikely to counterbalance the adverse effect of third generation contraceptives on venous thrombosis.