In summary, the development of intervention criteria is a complex and challenging endeavor. Specific examination of this issue is crucial to the appropriate clinical care of patients. With these objectives in mind, we have drawn upon our clinical experience to design, by way of statistical analysis, reasoned size criteria for intervention. These intervention criteria must be carefully weighed against the patient's age, overall physical condition, and anticipated life expectancy. We have approached the development of criteria for intervention using statistical methodology from the standpoint of preventing complications (i.e., dissection and rupture). Symptomatic states, organ compression, concomitant aortic insufficiency, and acute ascending aortic dissection are well-accepted general indications for surgical intervention regardless of aortic size. The appendix incorporates the size criteria developed in the present study as an integral component within a comprehensive strategy for managing patients with TAA. This study confirms that aneurysms of the thoracic aorta are potentially lethal, that attentive follow-up is critical, and that adverse events can be anticipated based on size criteria. As we continue to expand our database, we hope to refine further statistically-based recommendations for surgical intervention. Multi-institutional patient enrollment, with the concomitant statistical power of larger patient numbers, would considerably strengthen this type of analysis.