OBJECTIVE In the evaluation of the clinical impact of thrombotic diseases in young women, age-specific incidence rates must be calculated for both arterial and venous thrombotic diseases, but also the case-fatality rate and figures for the clinical consequences among those who survive thrombosis must be included. The aim of this analysis was to quantify the clinical impacts of both arterial and venous thrombotic diseases among young, nonpregnant women and thereafter to assess the influences of oral contraceptives on these measures. METHODS Nationwide register data on the morbidity and mortality of venous thromboembolism, myocardial infarction, and thrombotic stroke in Denmark, 1980-1993, and 3 ongoing case-control studies to assess the influence of oral contraceptives on the risk for development of these thrombotic diseases. RESULTS In women 15-29 years old venous thromboembolism is about twice as common as arterial complications, whereas in women 30-44 years old the number of arterial complications exceeds that of venous diseases by about 50%. The mortality rate from arterial diseases is 3.5 times higher than that from venous diseases among women <30 years old and 8.5 times higher than that from venous diseases in women 30-44 years old. The proportion of women with a significant disability among women who had an arterial complication was about 30%; the proportion was about 5% among women with venous thromboembolism. CONCLUSIONS Anticipating a differential influence on venous and arterial diseases from oral contraceptives with second- and third-generation progestogens, it was calculated that users of oral contraceptives with second-generation progestogens had 30% greater increased risk of thrombotic diseases, 260% greater increased risk of thrombotic deaths, and 220% greater increased risk of thrombotic disability than users of oral contraceptives with third-generation progestogens.