Objectives: The goal of this study was to determine the proportion of patients with left main coronary disease (LMCD) with unfavorable characteristics for percutaneous coronary intervention (PCI). Background: Published series suggest that LMCD can be treated percutaneously, however, the proportion of patients in whom PCI is an option based on angiographic criteria is unknown. Methods: In 13,228 consecutive coronary angiograms, 476 (3.6%) patients had >= 60% stenosis of the left main. In 232 patients with unprotected LMCD, the clinical characteristics and angiograms were reviewed with six features chosen as "unfavorable" for PCI: (1) Bifurcation LMCD, (2) occlusion of a major coronary, (3) ejection fraction <30%, (4) occlusion of a dominant RCA, (5) left dominant circulation, and (6) coexisting three-vessel disease. Treatment modality and 1 year mortality were determined. Results: The mean age was 69 years and 68% were male. Unfavorable characteristics were common with at least one unfavorable characteristic seen in 80%. Bifurcation disease was the most common unfavorable characteristic observed (53%) and coexisting three-vessel disease was seen in 38%. Treatment consisted of CABG in 205 (88%), medical therapy in 24 (10%) and PCI in 3 (1%). Among patients referred for CABG, 1 year survival was 88% with similar rates of survival for those with favorable characteristics (86%) compared to those with at least one unfavorable characteristic (88%). Conclusions: Most patients with LMCD have at least one unfavorable characteristic for PCI suggesting that PCI may be a technically difficult option for most patients with LMCD. (C) 2006 Wiley-Liss, Inc.