Objective: Endovascular abdominal aortic aneurysm repair (EAR) requires long-term surveillance for endoleak or increase in aneurysm diameter. We analyzed the natural history of and risk factors for endoleak development. Summary Background Data: Endoleak is a common complication of EAR that can lead to aneurysm enlargement and even rupture. Following EAR, imaging studies are used to identify leaks since patients with endoleak may require additional endovascular interventions or conversion to open repair. No criteria currently exist for cessation or reduction in frequency of screening imaging studies. Methods: Data on 220 patients undergoing EAR were retrospectively reviewed. Kaplan-Meier survival analysis and Cox proportional hazards regression were used with the end point being new endoleak development. Potential risk factors included preoperative aneurysm diameter, number of negative surveillance studies, and postoperative increase in diameter. Results: A total of 52 patients (24%) who underwent EAR had endoleak detected during postoperative follow-up, which averaged 19 months (range, 0.4-101 months). One, 6-, 12-, and 24- month endoleak-free survival was 90%, 80%, 77%, and 73%, respectively. Three leaks occurred after year 2, at postoperative months 24, 48, and 85. Increasing number of negative screening studies was negatively associated with risk for endoleak development (B = -3.122, P < 0.001), while increase in aneurysm diameter was positively associated with risk for endoleak (B = 0.072, P = 0.04). Conclusion: Risk for endoleak declines as the number of negative postoperative scans increases, but new endoleaks are identified as late as 7 years following EAR. Reduction in screening frequency cannot be uniformly recommended at this time. Patients with documented aneurysm expansion should be monitored carefully and endoleak should be suspected.