Circulating endothelial progenitor cells CD34+144+CD14- and CD34+VEGF-R2+CD14- have been shown to be inversely correlated to aortic aneurysm size. We aimed to see if aortic aneurysms could be followed-up by circulating endothelial progenitor cells CD34+144+CD14- and CD34+VEGF-R2+CD14- blood level. 40 patients followed for known aortic aneurysm >30mm and <50mm will be followed up every 6 months during 2 years. Each 6 months they will have a consultation by their physiologist with an echo or a CT-scan. At the same time, a 10ML blood sample will be taken to assess the circulating endothelial progenitor cells CD34+144+CD14- and CD34+VEGF-R2+CD14- blood level.