Introduction: It is unclear why severe isolated aorto-ostial stenosis was noted in women with relatively low atherosclerotic risks. The aim of this study was to elucidate that vascular and clinical characteristics of severe isolated aorto-main ostial stenotic lesion on intravascular ultrasound (IVUS) Methods: We divided total forty three patients (M:F=24:19, mean age=68짹12 ) into two groups. All the patients had significant stenosis at left main segment and underwent IVUS examination. Group 1 had isolated aorto- main ostial lesion without any other significant stenotic lesion. Group II had left main stenosis without significant involvement of main ostial area. Clinical characteristics and IVUS (Atlantis, Boston Scientifics, USA) parameters were compared. Result: The Group I patients were younger and had more female, less diabetes and high HDL level than Group IIpatients. But there were no significant differences in IVUS parameters for vascular evolutions (Figure) Conclusion: The patients with isolated aorto- main ostial lesion had less atherosclerotic burden than conventional left main diseased patients with involvement of entire main segment. It might be suggested that further study is mandatory to elucidate the pathogenesis of isolated aorto- main ostial lesion