Objective To evaluate the short-and long-term prevalence of persistent uncovered struts and in-stent thrombus after sirolimus-eluting stent(SES)implantation by optical coherence tomography (OCT).Methods OCT was performed for 31 SES in 21 patients at 3 months and for 30 SES in 21 patients at 2 years post SES implantation.Thickness of new intima inside each strut was measured and thickness equal to 0 μm was defined as an uncovered strut.Existence of in-stent thrombus was also evaluated.Results A total of 4545 struts and 3707 struts were evaluated at 3 months and at 2 years post SES implantation,respectively.New intima at 2 years was significantly thicker than that at 3 months[(71±93)μm vs.(29±41)μm,P＜0.01].Percent of uncovered struts at 2 years was significantly lower than that at 3 months(5%vs.15%,P＜0.01).Prevalence of uncovered struts was similar at 2 years and at 3 months(81%vs.95%,P＞0.05).subclinical thrombus was recognized in 14%patients at 3 months and 2 years post SES implantation.Conclusions Neointimal coverage inside the SES is a continuous process and the number of uncovered struts decreased from 3 months to 2 years after SES implantation.Few uncovered struts could still be visualized in the majority of patients at 2 years post SES implantation.