As a result of abnormal flow patterns and hyperdynamic flow in arteries proximal to an arteriovenous fistula a particular susceptibility to atherosclerotic changes and aneurysmal deterioration develops. In the following report two patients are presented in which chronic arteriovenous fistulas existed for 15 and 33 years prior to correction. Each patient developed extensive and progressive aneurysmal dilation of the proximal arterial tree and subsequently required surgical resection and graft replacement.