and Purpose-We sought to determine the incidence and severity of bleeding events in patients with stroke and cardiovascular diseases who were taking oral antithrombotic agents in Japan, where the incidence of hemorrhagic stroke is higher than in Western countries. Methods-A prospective, multicenter, observational study was conducted; 4009 patients who were taking oral antithrombotic agents for stroke and cardiovascular diseases were enrolled. The patients were classified into 4 groups according

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... to their antithrombotic treatment: the single antiplatelet agent group (47.2%); the dual antiplatelet agent group (8.7%); the warfarin group (32.4%); and the warfarin plus antiplatelet agent group (11.7%). The primary end point was life-threatening or major bleeding according to the MATCH trial definition. Results-During a median follow-up of 19 months, there were 57 life-threatening and 51 major bleeding events, including 31 intracranial hemorrhages. The annual incidence of the primary end point was 1.21% in the single antiplatelet agent group, 2.00% in the dual antiplatelet agent group, 2.06% in the warfarin group, and 3.56% in the warfarin plus antiplatelet agent group (PϽ0.001). After adjustment for baseline characteristics, adding an antiplatelet agent to warfarin increased the risk of the primary end point (relative riskϭ1.76; 95% CI, 1.05 to 2.95), and adding another antiplatelet agent to single antiplatelet agent therapy increased the secondary end point of any bleeding, including minor events (relative riskϭ1.37; 95% CI, 1.07 to 1.76). Conclusions-The incidence of bleeding events during antithrombotic therapy in Japan was similar to that reported for Western countries, although the trials used different study designs. Dual antithrombotic therapy was independently related to an increased risk of bleeding events. (Stroke. 2008;39:000-000.)