Although the incidence of thoracic aortic aneurysm is on the rise, initial imaging diagnosis can present a challenge for many clinicians. Providers are faced with many imaging choices as part of the initial workup. Considering level of invasiveness, relative radiation level, and quality of associated diagnostic data, CT angiography and MR angiography are believed to be the most appropriate options for radiological diagnosis of suspected thoracic aortic aneurysm. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.