We describe a 41-year-old woman with no cardiac risk factors, typical exertional angina and an abnormal noninvasive stress test. Coronary angiography demonstrated an ambiguous left main coronary artery (LMCA) stenosis. Intravascular ultrasound (IVUS) demonstrated no atheroma, but the minimum lumen diameter and area of the ostial LMCA were significantly reduced. Transesophageal echocardiography showed normal left ventricular function with a bicuspid aortic valve. Two-vessel coronary artery bypass grafting was subsequently performed. To our knowledge, this is the first IVUS-documented case of a congenital left main coronary artery stenosis associated with a bicuspid aortic valve. © 2006 HMP Communications.