Objectives: To assess outcomes and develop duplex scan criteria that will reliably determine the luminal status of covered and uncovered renal stents following fenestrated and branched endovascular repair. Methods: A prospective database of patients treated with fenestrated and branched endografts between 2001 and 2006 was reviewed. All patients with evidence of renal artery pathology including duplex scan assessed peak systolic velocity (PSV) <50 or >200 cm/s, renal aortic ratio (RAR) >3.5, elevation of the serum creatinine >30%, computed tomography (CT) evidence of renal stenosis underwent further analyses including medical chart review, and a review of CT and duplex scan imaging data. Correlations of ultrasound scan, CT, angiographic, and clinical outcomes were conducted and receiver operator curve (ROC) analysis was performed. Freedom from stenosis or occlusion was determined by Kaplan-Meier analysis with differences assessed by log rank tests. Results: A total of 518 renal arteries were treated with uncovered or covered renal stents (287 patients). Mean follow-up was 25 months. The estimated freedom from stenosis at 12, 24, and 36 months were 95% (95% confidence interval [CI] 93-98), 92% (89-96), and 89% (85-93) for uncovered stents, and 98% (96-100), 97% (95-100), and 95% (91-100) for covered stents (log rank P = .04). Secondary interventions were performed in 20% of the patients who developed stenoses. Only one of the detected stenoses that was not treated with a secondary intervention progressed to occlusion. Duplex scan criteria derived from ROC analysis correlating with curved planar reconstruction (CPR) from axial imaging data calculated a 60-99% in-stent stenosis to be associated with a PSV >280 cm/s or RAR >4.5. Occlusions were best identified by a mid renal artery PSV <57 cm/s in conjunction with an RAR <1.2. Conclusion: Revised ultrasound scan criteria have been developed to improve the sensitivity and specificity of non-invasive interrogation of renal stents following endovascular aneurysm repair (EVAR). Covered renal stents are associated with a lower incidence of in-stent stenosis and are thus recommended over uncovered stents for use in fenestrated or branched endografts.