Atherosclerosis is an inflammatory condition where cysteinyl leukotrienes have been identified to play an important role. Furthermore, cysteinyl leukotrienes may also affect thrombus formation. Using prospective, cross-sectional and case-control designs, we tested the hypothesis that hitherto unknown genetic variation, likely to affect the function of leukotriene C(4) synthase, is associated with risk of venous thromboembolism, ischemic stroke and myocardial infarction.