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OBJECTIVES: After elective aortic valve replacement, patients are at risk of developing valve thrombosis and systemic arterial thromboembolism. Current guidelines recommend antithrombotic therapy with aspirin or vitamin K antagonists (VKAs) during the first 3 months after the procedure, but have level 2 or 3 evidence. As a consequence, the most appropriate antithrombotic therapy is still a matter of debate. This retrospective study analysed all thromboembolic and bleeding complications in patients with either antiplatelet or anticoagulation therapy 1 year after bioprosthetic aortic valve replacement. METHODS: A total of 402 patients undergoing bioprosthetic aortic valve implantation at the VU University Medical Centre and subsequently treated at three regional hospitals were included. The individual duration of either VKAs (acenocoumarol) or aspirin was determined and related to thrombotic and bleeding events. Patients were followed and censored at 1 year postoperatively for survival, cerebral ischaemia, myocardial infarction, peripheral arterial embolism, and minor and major haemorrhages. RESULTS: A total of 24 thromboembolic complications and 31 bleeding episodes occurred. Multivariable analyses revealed that acenocoumarol caused more bleeding episodes (risk ratio [RR]: 8.41, 95% CI: 3.58-19.79) and a similar amount of thromboembolic events (RR: 1.2, 95% CI: 0.47-3.02) compared with aspirin. Prior use of acenocoumarol was found to be a risk factor for thromboembolic events (RR: 3.1, 95% CI: 1.31-7.19). Gender, dyslipidaemia, prior percutaneous coronary intervention, prior use of acenocoumarol and concomitant coronary artery bypass grafting were found to be predictors for bleeding events. CONCLUSIONS: In patients 1 year following bioprosthetic aortic valve replacement, acenocoumarol therapy was associated with a significant increased risk of bleeding events and no reduction in thromboembolic events compared with antiplatelet therapy. These findings support the recommendations of aspirin over VKAs as postoperative thromboprophylaxis. [ABSTRACT FROM AUTHOR]