The clinical utility of aspirin in the management of venous thromboembolism is a matter of debate. The Pulmonary Embolism Prevention Study 11 demonstrated that 35 days of low-dose aspirin (160 mg daily) compared with placebo reduced the risk of symptomatic venous thromboembolism, including fatal pulmonary embolism, by about one-third (RRR 36%, 95% CI: 19-50%, p=0.0003) in patients undergoing emergency surgery for hip fracture or elective joint arthroplasty. There was no excess of fatal or intracranial bleeding. In the Heart and Estrogen/progestin Replacement Study (HERS)12 2800 postmenopausal women with coronary artery disease were randomized to hormonal replacement therapy or placebo. A secondary analysis showed that the use of aspirin was independently associated with a 50% reduction (95% CI: 20-80%) in risk of venous thromboembolism during an average of 4.1 years of follow-up. Taken together, these data suggest that aspirin reduces the risk of a first episode of venous thromboembolism by about one-quarter (i.e., 25% risk reduction).