A case of a mycotic false aneurysm of the ascending aorta and aortic sinus caused by coagulase-negative staphylococcal endocarditis following the placement of a Starr-Edwards prosthesis for rheumatic aortic stenosis is reported. The formation of the aneurysm caused aortic insufficiency, and terminally the prosthesis was torn from the aorta. The occurrence of mycotic aneurysms in the aorta and their etiology and pathogenesis are discussed. Cases of postoperative false-aneurysm formation of the ascending aorta are reviewed.