We report a rare case of bicuspid aortic stenosis complicated by an ascending aortic aneurysm and aortic dissection of DeBakey type IIIb. A 35-year-old woman was admitted to our hospital to examine her systolic murmur identified at birth. Severe aortic stenosis, dilatation of the ascending aorta, and the narrow color flow signal in the descending aorta were detected by transthoracic echocardiography. Initially, coarctation of the descending aorta was suspected, but aortic dissection, DeBakey type IIIb, was revealed by transesophageal echocardiography. Transesophageal echocardiography is indicated when only insufficient information is available on valve and aortic morphology in patients with bicuspid aortic valve.