Background The long-term (10-year) comparative results of patients with unprotected left main coronary artery (LMCA) disease who underwent coronary stenting or coronary-artery bypass grafting (CABG) are unknown. Methods Between January 1995 and April 1999, 350 patients with unprotected LMCA disease underwent stent implantation (n=100) or CABG (n=250). The primary safety end points were all-cause mortality and the composite of death, Q-wave myocardial infarction (MI), or stroke, and the primary efficacy end point was target-vessel revascularization (TVR). Results In a crude analysis, the 10-year rates of death (15.9% for PCI vs. 24.1% for CABG; P=0.02) and the composite of death, Q-wave MI, or stroke (25.2% for PCI vs. 32.1% for CABG; P=0.04) were significantly lower in patients who received stenting than in those who underwent CABG. However, after adjustment for baseline risk factors, the overall risks of death (hazard ratio 0.68; 95% confidence interval [CI] 0.36 to 1.30; P=0.24) and the composite of death, Q-wave MI, or stroke (hazard ratio 0.90; 95% CI 0.54 to 1.50; P=0.69) were similar between the 2 groups. The rate of revascularization was significantly higher in the PCI than in the CABG group (hazard ratio 11.35, 95% CI 4.90 to 26.31; P<0.001). Conclusions At 10-year follow-up of patients with unprotected LMCA disease, we found no significant difference in rates of death or of the composite end point of death, Q-wave MI, or stroke between patients receiving stents and those undergoing CABG. However, stenting was associated with higher rates of TVR than was CABG.