Thoracic aortic aneurysm (TAA) is a silent disease that can become rapidly lethal once dissection or rupture occurs. To prevent aortic catastrophe, prophylactic aortic replacement is the mainstay of therapy in patients with TAA. Currently, surgical indications for TAA repair are predominantly based on the aortic size. However, the effectiveness of the diameter criterion to predict aortic rupture and dissection has been largely questioned over the last years. Growing evidence suggests that aortic size alone may not be sufficient to predict the risk in all TAAs. In this setting, other predictors such as genetic, environmental, biochemical and hemodynamic factors have been proposed. The aim of this paper is to review and discuss on current evidence, controversies and future directions for the treatment of patients with TAA.