Subjects will undergo an evaluation of the Valiant endoluminal stent-graft to determine the safety and efficacy of the device as indicated by the adverse event rate, and to determine the risk factors that are most predictive of a successful outcome when used to exclude thoracic aortic aneurysms that require suprarenal fixation in high risk and low risk patients. Follow-up will be completed at 1, 6, 12, 24, 36, 48, and 60 months. Subject evaluation at 1 month will include a Complete Physical Exam, Labs (BUN and Creatinine), and a Thoracic Spiral CT with and without IV contrast 2.5 mm. Subject evaluation at 6, 12, 24, 36, 48, and 60 months will include a Complete Physical Exam, Chest X-ray (AP, Lateral), Labs (BUN and Creatinine), and a Thoracic Spiral CT with and without IV contrast 2.5 mm.