Background Moderate left main coronary artery (LMCA) disease is known to be associated with future cardiac events and the long-term prognosis of patients undergoing percutaneous coronary intervention (PCI) of LMCA stenosis was favorable in selected patients. However, outcomes of intermediate LM ostial lesion stenting by have not been clearly defined, thus this study was performed to evaluate the outcome of patients with angiographically intermediate LMCA stenosis undergoing PCI. METHODS AND RESULTS: We analyzed data from all PCIs performed from August 1996 to June 2005 in the LMCAs and compared LM ostial with uncovered LM ostial PCI outcomes. Of 132 consecutive patients who underwent PCI of LMCA, 45 patients were found to have LM ostial narrowing and 97 patients nonostial narrowing. Patients with angiographically intermediate lesion had 2-dimensional IVUS imaging. Baseline characteristics were similar between the 2 groups. Stenting occurred in 96% of all patients and was similar in patients with ostial or nonostial narrowings. Procedural success was similar (100% vs. 95%, p = 0.95) and percent diameter stenosis by angiography was the same for ostial and uncovered ostial PCI 54짹27% and 56짹19%, respectively. IVUS mean minimal luminal area (MLA) was 5.0짹2.1mm2 and 8.4짹5.5mm2, respectively. Six-month event-free survival rate tend to be lower in patients who underwent ostial PCI (96% vs. 86%, p = 0.237), with a same need for repeat PCI or CABG (15% vs. 10%, p=0.517). CONCLUSIONS: PCI of Intermediate LMCA ostial lesion on angiography was relatively safe without significant different luminal changes with PCI of uncovered LMCA ostial lesion.