Long-term follow-up of controlled clinical trials of endovascular grafting for aortic aneurysms will provide data on the safety and efficacy of this new treatment to reduce morbidity and mortality compared with standard treatment. It will be several years before this information will be available, and careful analysis of surrogate markers for clinical success has value for predicting long-term outcome. One essential surrogate marker is aortic aneurysm diameter, which has traditionally been the most important variable in calculating rupture risk, and multiple studies have shown that aneurysms shrink after complete endovascular exclusion. Furthermore, measurements of aortic neck size and aortic length has shown interesting patterns that may affect the durability of endovascular repair and, thus, may suggest potential strategies for the design of future devices.