Endovascular aortic repair (EVAR) offers shorter hospitalizations and improved short-term morbidity and mortality rates than traditional open surgical repair (OSR), particularly in the elderly. EVAR does have a number of known complications, some that are particular to the endovascular approach and some that are shared with OSR, especially in a patient population frequently afflicted with a heavy comorbidity burden. These complications encompass the entire spectrum, from transient, minor problems to those that threaten life and limb. This chapter discusses endoleak, a complication unique to endovascular aneurysm repair, which is defined as persistent blood entry into the aneurysm sac following EVAR. Endoleaks are classified into five categories, types I through IV and endotension; the category aids in determining the appropriate treatment and its urgency. Other complications include graft occlusion, ischemic complications, postoperative renal insufficiency and renal artery occlusion, late rupture, and infectious complications.