Background and Objectives: Stent thrombosis(ST) is a serious adverse event commonly associated with sudden death or acute myocardial infarction. There are several data about stent thrombosis from randomized clinical trial, but these findings could not be applicable to the real-world clinical setting. The aim of this study was to evaluate the incidence, clinical characteristics, and clinical outcome of ST after implantation of DES in real world clinical practice. Methods: This was a retrospective single center study. PCI was performed in 1512 patients with coronary artery disease. The 1032 patients who underwent successful DES implantation (1163 lesions, 1290 DES) between January 2005 and May 2007 were investigated. Results: The incidence of definite (angiographically proven) thrombosis was 0.9% (total 9 patients, 4 patients in Cypher group(0.6%), 2 patients in Taxus group(0.4%), 3 patients in Endeavor group(2.8%)). The incidence of definite or probable as defined by the Academic Research Consortium was 1.1% (4 patients in Cypher group(0.6%), 2 patients in Taxus group(0.4%), 5 patients in Endeavor group(4.6%)). Acute ST was in 1 patient (0.1%, 1 patient in Endeavor group), subacute ST was in 5 patients (0.48%, 1 patient in Cypher, 1 patient in Taxus, 3 patients in Endeavor group), late ST was in 4 patients (0.3.9%: 2 patients in Cypher, 1 patient in Taxus, 1 patient in Endeavor group) and very late in 1 patient(0.1% : 1 patient in Cypher group). Most of ST patients pre-interventional clinical presentation was acute coronary syndrome(ACS)(8 of 11 patients) and multivessel disease(7 of 11 patients). The initial clinical presentation of definite ST was ST elevation MI (6 patients), non ST elevation MI (1 patient), Angina pectoris (2 patiets). Four patients were died of ST (1 patient in Cypher, 1 patients in Taxus , 2 patients in Endeavor group). Conclusions: The incidence of ST is higher in patients with ACS than stable angina. The incidence of ST after successful Endeavor stent implantation in real-world patients was higher than the rate reported in clinical trials. It is possible that the patients of real world practice are more complex lesion and severe condition than the patients of large randomized trial.