Background;Dual or triple antiplatelet therapy is generally recommended in patients undergoing percutaneous coronary intervention with stent implantation(PCI-S). After PCI-S in case taking chronic anticoagulation(AC), practice guidelines about the antithrombotic strategies are lacking and there have been concern about high risk of bleeding associated with the combined administration of dual or triple antiplatelet therapy and chronic AC. Objectives; The aim of our study is to evaluate the practice realities of antithrombotic treatment adopted following PCI-S patients taking chronic AC at our institution and to evaluate the safety of dual or triple antiplatelet therapy combined with chronic AC in patients who had indication for long-term AC. Methods; 131 patients who underwent PCI-S with an indication for long-term anticoagulation was included in this analysis (single center, Mar. 2000 to Dec. 2008). The mean follow-up period was 37.0짹23.5 months. Results; Of the 131 patients, 67% were men, with a mean age of 67.1짹9.6 years. Indications for chronic AC were as follows: atrial fibrillation;n=103(78%), prosthetic valve;n=11(8.3%), LV thrombus;n=7(5.3%), pulmonary thromboembolism;n=4(3.0%). Drug-eluting stents were implanted in 97(73.5%), and bare-metal stent(BMS) were implanted in 34(26.5%). Among the 131 patients, 12 patients (9.1%) initially took aspirin(A)+plavix(P1)+ pletaal(P2)+warfarin(W), 116 patients (88.6%) did A+P1+W, 3 patients(2.3%) did A+W. The mean triple therapy (A+P1+W) duration was 8.9짹6.2 months and that of quatriple therapy (A+P1+P2+W) was 3.1짹2.8 months. During the triple therapy (A+P1+W) following initial quadriple therapy (A+P1+P2+w), 2 patients (1.5%) developed major bleeding and of them, 1 patient died of ICH. During initial triple therapy (A+P1+W), 2 patients (1.5%) developed major bleeding. During the dual therapy following initial triple therapy, 5 patients(3.8%) developed major bleeding and of them, 1 patient died of UGI bleeding. Except for 2 cases, all of other events happened below the therapeutic range of INR. Conclusions; Major bleeding complications developed in 9 patients (6.9%) taking dual or triple antiplatelet therapy with warfarin and 2 cases were lethal. The most events happened below the theraputic range of INR. In the future, large-scale, randomized, prospective study about proper antithrombotic strategies in this groups is required.