Annular subvalvular left ventricular aneurysm is a rare cardiac malformation occurring predominantly in blacks, and the developmental aspects of this malformation are not known. In Korea there has been one case report accompanied with subacute bacterial endocarditis. We experienced a case of subannular aortic aneurysm with bicuspid aortic valve in a 21-year-old man who had been diagnosed as subacute bacterial endocarditis. To our knowledge, this is the fourth report in the world of subannular aortic aneurysm with congenital bicuspid aortic valve. We speculate about the cause of the malformation in our patient. The deformed bicuspid aortic valve may have caused high pressure in the left ventricle, and the associated congenital disorder of the connective tissue in the wall near the atrioventricular groove may have caused herniation of the endocardium and formation of a subannular aortic aneurysm under this high pressure.