Despite significant improvements in surgical techniques and perioperative management, the repair of descending thoracic aortic aneurysms remains a challenge with the potential for substantial morbidity and mortality. Over the past several years, buoyed by the technical success of endovascular repair of infrarenal abdominal aortic aneurysms, several case series reports of endovascular stent-graft placement for descending thoracic aortic aneurysms have demonstrated the potential safety and efficacy of this treatment modality. Several single-institution studies have documented promising results with these devices, but without controlled clinical trials, the data are insufficient to determine if thoracic aortic endografts provide equivalent or improved outcomes compared with standard open repair. We describe a study design of an ongoing prospective, nonrandomized, multi-institutional, investigational device exemption phase II pivotal clinical trial investigating the safety and effectiveness of the Zenith TX2 thoracic aortic endovascular graft in the elective treatment of patients with descending thoracic aortic aneurysms.