Objective To determine the incidence and risk factors of stent thrombosis(ST) after sirolimus-eluting stent(SES) implantation.Methods A total of 156 patients who received percutaneous coronary intervention procedure with SES implantation between Apr 2006 to Aug 2007 in our hospital were evaluated.Angiographic and procedural outcome were documented by interventional cardiologist,the clinical outcome was recorded before discharge.Clinical follow-up was carried out for 6 months in 72 patients and for 1 year in 84 patients,to investigate the incidence,risk factors and outcome of ST.Results Four patients had suffered from ST: 3 patients(1.92%) were early ST,1 patient(0.64%) was late ST.From the 4 patients there were 2 multivessel diseases,2 bifurcation lesions and 2 long diffuse lesions patients.Six stents were implanted,mean stents diameter was(2.88±0.38)mm,mean stents length was(25.5±6.12)mm and mean release pressure of stents was(13.33±1.03)atm with 1 high-pressure post-dilation,TIMI grade 3 flow was achieved after procedure in all 4 patients.One patient presented acute ST-elevation myocardial infarction 3d after procedure and received rt-PA and IABP treatment,now survives without any events;3 patients suffered from sudden death 6 d,15d and 81d after the procedure respectively.Conclusion In our study,3 developed early ST and 1 late ST in 156 patients after SES implantation.The clinical presentation is acute myocardial infarction or sudden death.The development of ST after SES implantation is probably associated with the following factors:(1) acute coronary syndrome with multivessel diseases,bifurcation lesions or long diffuse lesions;(2) the presence of residual dissection or stent under-expansion without intravascular ultrasound assessments.Coronary ST is a catastrophic complication after percutaneous coronary intervention,and the mortality is high.