Background: Despite the substantial benefit of drug-eluting stents(DES) on the neointimal growth suppression, the long-term safety regarding stent thrombosis(ST) has been questioned recently. Data on the difference of the incidence of ST between acute coronary syndrome(ACS) and stable angina are limited in patients with implantation of DES. Methods: We identified 3,153 patients who underwent DES implantation at our institution between Feb.2003 and Mar.2006, in whom 1,494 patients(47%) were presented with stable angina and 1,584 patients(53%) with ACS. The clinical outcomes up to 3 years for ST were compared after the adjustment for differences in baseline characteristics. Results: Stent thrombosis occurred in 66 patients (the cumulative incidence of ST upto 3 years=2.1%). ST was more developed in patients with ACS, as compared with those with stable angina(44/1,584pts (2.8%) vs. 22/1,494pts (1.5%), p=0.013). Mean durations of development of ST in stable angina and ACS group were 30.1짹9.7 and 28.9짹10.5 months. Cox-regression analysis showed that the incidence of ST in patients with ACS was significantly higher than that of patients with stable angina according to time duration(any ARC: p=0.049, HR=1.94 ; 95%, CI 1.10-3.74, definite or probable ARC: p=0.046, HR=3.319, CI 1.02-9.63). Conclusion: Our data demonstrated that long-term cumulative incidence of ST was significantly higher in ACS group than in stable angina group. This suggests that pharmacological or mechanical effort may be needed to prevent ST in patients with ACS after DES implantation.