Background: Endovascular repair for abdominal aortic aneurysm (EVAR) requires regular surveillance to ensure long-term durability. To understand the clinical consequence of discrepancies in endoleak detection between computed tomographic angiography (CTA) and duplex ultrasound (DUS) imaging, this study evaluated patients who underwent EVAR. The aim of the present study was to determine whether these discrepancies affected the long-term outcome after EVAR, and whether DUS predicted the need for re-intervention on the basis of other markers despite missing endoleaks. Methods: A review of the prospectively maintained database was completed to capture all EVAR procedures performed between October 1999 and June 2009. Patients were routinely evaluated with computed tomography (CT) and DUS imaging within 30 days after the procedure and intermittently at 6-12 month intervals after treatment. DUS imaging was evaluated with attention toward maximum aneurysm diameter, presence of an endoleak, and compared with findings on simultaneous contrast CT imaging. Results: The database and patient records identified 1,062 EVARs in 992 patients who underwent 3,120 imaging encounters through the surveillance protocol. Of these 3,120 encounters, 610 had both CT scan and ultrasound at the same visit. Contrast material was not used in 49 CT scans, leaving 561 encounters for comparing contrast CT imaging with DUS results. CT and DUS detection of endoleaks correlated in 442 encounters (78.8%). Discrepancies occurred in 119 encounters (21.2%) as follows: CT scan only endoleak in 17.8% (N = 100; type I = 6, type II = 91, and type III = 3) and DUS only endoleak in 3.4% (N = 19; type II = 19) encounters. Of these 119 encounters, 99 (17.6%) did not require secondary interventions. Eventually, 15 patients required intervention after 20 discrepancy encounters (3.6%): 11 patients continued with the surveillance protocol through CT or DUS imaging, whereas four were observed by CT imaging only. Considering these 11 patients, DUS eventually detected an endoleak on subsequent visits in five patients, DUS identified an increase in aneurysm diameter in four patients, and DUS never identified the type II endoleaks in two patients. When the endoleak raised concern or the aneurysm enlarged, we undertook 19 secondary interventions in these 15 patients: vessel embolization (N = 8), iliac extenders (N = 5), graft relining (N = 3), graft explants (N = 2), and proximal cuff (N = 1). Although three ruptures occurred in our entire treatment experience, no ruptures occurred in patients who maintained the prescribed surveillance protocol. Conclusion: Surveillance after EVAR is necessary because secondary interventions are sometimes required. Although DUS has lower sensitivity in detecting endoleaks, comparison with CT findings can identify the appropriate patients for DUS surveillance only. Even considering the discrepancies between CT imaging and DUS, repeated DUS surveillance might identify an unstable aneurysm that requires further intervention. Although DUS has not been established as an exclusive surveillance tool, it can be used to effectively monitor patients after EVAR with reduced need for CT imaging. © Annals of Vascular Surgery Inc.