Endovascular repair for abdominal aortic aneurysms (EVAR) has evolved as a common treatment for this disease entity. Although it provides outstanding early and mid-term results, the use of EVAR requires vigilant follow-up to insure that delayed complications - such as endoleaks-do not complicate an initially successful procedure. The optimal modality for detection of this entity remains undetermined. We present the case of a 77-year-old woman with a type I proximal endoleak identified on duplex ultrasound examination 1 month postoperatively. It was confirmed with computed tomography scanning and contrast aortography. The diameter of the aneurysm sac had increased from 5.8 cm (preoperatively) to 6.0 cm, prompting consideration of an intervention to address the endoleak. Repeat duplex examination, performed immediately before the planned repair, failed to demonstrate the endoleak, and the aneurysm sac measured 5.6 cm. This case report demonstrates the ability of duplex ultrasound to identify endoleaks and its importance in the close follow-up of patients who have undergone EVAR.