Background: The feasibility of PCI for unprotected left main coronary artery stenosis(LMCAS) has been demonstrated previously in the BMS era. DES has improved outcomes of PCI especially with regard to repeat revascularization. However, long term outcome after DES implantation in patients with unprotected LMCAS is scarce. To evaluate the mid to long term clinical outcome of such patients, we performed a retrospective analysis of a two center registry from the Seoul National University Main and Bundang Hospital.Methods: We consecutively enrolled all patients with unprotected LMCAS receiving DES from Feb 2003 to June 2006. These patients had at least 1 year of follow-up. Baseline demographic and angiographic data as well as in-hospital and clinical outcome up to June 2007 was analyzed.Results: We identified 160 patients with unprotected left main disease that received DES implantation. 69% of the patients were male, 40% had DM, 63% had hypertension, 52% were smokers, and 45% had dyslipidemia. The mean age of the patients was 64.7짹11.4 years. Approximated 47% of the patients had unstable angina or NSTEMI, 34% had stable angina, and 11% had STEMI. IABP was used in 11% of the cases and Gp IIb/IIIa inhibitors were used in 7.5% of the patients. Bifurcation involving lesions comprised 71% of the lesions. The most common method of stent deployment was crossover(42%) or single stent within the left main(22%) followed by kissing stent(14%) crush (11%), and T stenting(11%). Kisssing balloon inflation was performed in 61% of the cases.Procedural success rate was 98.8% and inhospital death rate was 4.4%. Except for 5 patients who were lost during follow-up, 155 patients were followed for at least 1year and the mean duration of follow-up was 22.5짹11 months. At six months, the cumulative CV death rate was 5.7% with TLR rate 8.2% and TVR rate 13.3%. This increased to 6.4%, 9%, and 14.7% respectively at 1year. At final follow-up, the rate of cumulative all cause death was 14.3%, CV death 10.5%, cumulative TLR 9.7%, and TVR 17.5%. The rate of stent thrombosis(ST) was 3.2% when using the ARC definite and probable ST classification and 7.1% when including possible ST.Conclusion: PCI for LMCAS using DES showed good peri-procedural outcome with acceptable rates of MACE up to nearly 2 years. However, the continued cumulative annual occurrence of cardiac death and TVR warrants caution and therefore even in the era of the DES, PCI for unprotected LMCAS should be reserved for high surgical risk patients or those who refuse surgery, and should be weighed against the risk and benefits of surgery.