Objectives: This study sought to assess percutaneous coronary intervention (PCI) for unprotected left main coronary artery (ULMCA) stenosis in routine U.S. clinical practice. Background: Percutaneous coronary intervention for ULMCA stenosis is controversial; however, current use and outcomes of ULMCA PCI in routine U.S. clinical practice have not been described. Methods: We evaluated 5,627 patients undergoing ULMCA PCI at 693 centers within the National Cardiovascular Data Registry Catheterization Percutaneous Coronary Intervention Registry for temporal trends in PCI use (2004 to 2008), patient characteristics, and in-hospital mortality. Thirty-month mortality and composite major adverse events (death, myocardial infarction, and revascularization) with drug-eluting versus bare-metal stents were compared using inverse probability weighted (IPW) hazard ratios (HRs) in a nonrandomized Medicare-linked (age <65 years) patient cohort (n = 2,765). Results: ULMCA PCI was performed in 4.3% of patients with ULMCA stenosis. Unadjusted in-hospital mortality rates ranged from 2.9% for elective cases to 45.1% for emergent/salvage cases. By 30 months, 57.9% of the elderly ULMCA PCI population experienced death, myocardial infarction, or revascularization, and 42.7% died. Patients receiving drug-eluting stents (versus bare-metal stents) had a lower 30-month mortality (IPW HR: 0.84, 95% confidence interval [CI]: 0.73 to 0.96), but the composite of major adverse events were similar (IPW HR: 0.95, 95% CI: 0.84 to 1.06). Conclusions: In the United States, ULMCA PCI is performed in <5% of patients with ULMCA disease and is generally reserved for those at high procedural risk. Adverse events are common in elderly patients and are related to patient and procedural characteristics, including stent type. © 2012 American College of Cardiology Foundation.