Congenital atresia of left main coronary ostium is a rare congenital coronary anomaly. This anomaly was detected during elective coronary angiogram in a 40 year-old female patient with chest pain and exertional dyspnea. Treadmill exercise test demonstrated 2 mm upslope depression of ST segment at stage I and the test was terminated due to chest pain. Myocardial stress SPECT using 201 Tl-dipyridamole showed reversible perfusion defects at anterior, apex and lateral wall. It was impossible to select left coronary artery ostium and right coronary angiogram revealed 30% eccentric stenosis at proximal right coronary artery with grade 3 collateral flow to left anterior descending and circumflex arteries. Operative finding revealed totally occluded left coronary ostium with membrane-like, non-atheromatous tissue similar to aortic wall. The patient was successfully treated with coronary artery bypass grafts (CABG) using left internal mammary artery and great saphenous vein. She underwent follow-up coronary angiogram, which revealed patent grafts, at one year after CABG and no cardiovascular event was observed on 5-year clinical follow-up.