The aim of this study was to compare long term clinical outcome after left main stenting in a large real world population of patients treated with drug-eluting stents (DES) or bare-metal stents (BMS) in the setting of acute coronary syndromes. The advent of DES decreased the risk of unprotected left main coronary artery restenosis as compared with BMS, but safety concerns still exist, especially when high-risk patients presenting with acute coronary syndromes are considered. The Gruppo Italiano Studi Emodinamici-Societa' Italiana di Cardiologia Invasiva (GISE-SICI) registry is a retrospective, observational multicenter registry promoted by the Italian Society of Invasive Cardiology in which 19 high-volume participating centers enrolled 1,453 consecutive patients who underwent percutaneous coronary intervention on unprotected left main coronary artery between January 2002 and December 2006. From the registry, a total of 849 consecutive patients presenting with unstable angina or non-ST-segment elevation myocardial infarction who underwent DES (n=611) or BMS (n=238) implantation were analyzed with extensive multivariable and propensity-score adjustments. At 3-year follow-up, the adjusted hazard ratio for the risk of mortality after DES implantation relative to BMS implantation was 0.90 (95% confidence intervals [CI] 0.59 to 1.38, p=0.617), and the adjusted hazard ratio for the risk of cardiac mortality was 0.75 (95% CI 0.45 to 1.27, p=0.287). DES were associated with significant reduction of myocardial infarction (hazard ratio 0.37, 95% CI 0.17 to 0.81, p=0.009) and target lesion revascularization rates (hazard ratio 0.38, 95% CI 0.21 to 0.69, p=0.001). Younger age, low ejection fraction, an increase in the cardiac biomarkers, absence of diabetes, and bifurcations showed a significant interaction with assigned treatment regarding myocardial infarction. The treatment effects on target lesion revascularization were consistent across multiple subgroups, with the possible exception of patients with nonbifurcational lesions. In conclusion, in a large population of patients with acute coronary syndromes and unprotected left main coronary artery disease DES were more effective than BMS in reducing myocardial infarction and target lesion revascularization. There was no evidence of a significant reduction in mortality with DES versus BMS.