The purpose of the present study was to assess the outcomes of fenestrated-branched endovascular aortic repair (FB-EVAR) using infrarenal aortic vs iliac sealing zones. We reviewed the clinical data of 430 consecutive patients enrolled in a prospective nonrandomized study to evaluate FB-EVAR from 2013 to 2020. The outcomes were analyzed for patients with extent I to IV thoracoabdominal aortic aneurysms who had undergone FB-EVAR with distal implantation in the native infrarenal aorta. The minimum anatomic criteria for the use of infrarenal aortic seal was a >3-cm length of parallel aorta with a diameter of 18 to 32 mm without excessive thrombus or calcification. A control group matched for the extent of aortic disease with an iliac artery seal was used to compare the following endpoints: 30-day mortality, major adverse events, freedom from type Ib endoleak (TIbE), freedom from secondary interventions, and changes in the infrarenal aortic diameter. A total of 110 patients (55 men; mean age, 73 ± 8 years) were included in the present study, 55 with an infrarenal aortic distal seal and 55 with the iliac arteries as the sealing zone. Both groups had similar clinical characteristics and aneurysm extent and diameter, except for a greater number of men and higher serum creatinine in the iliac seal group. Technical success was obtained in 106 patients (96%) and was greater for the iliac sealing zone group (100% vs 93%; P = .04). The use of the infrarenal aortic sealing zone was associated with shorter endovascular (148 ± 56 minutes vs 191 ± 61 minutes; P < .001) and fluoroscopy (76 ± 28 minutes vs 96 ± 32 minutes; P < .001) times and lower radiation exposure (cumulative air kerma, 1.4 ± 1.4 Gy vs 2.1 ± 2.0 Gy; P = .02; dose area product, 147 ± 75 Gy ∙ cm2 vs 208 ± 102 Gy ∙ cm2; P = .006). One patient had died (1%) within 30 days. No differences were found in the major adverse events among the patients treated with infrarenal aortic vs iliac sealing zones (22% vs 18%; P = .63), including any spinal cord injury (13% vs 9%; P = .54) and grade 3 spinal cord injury (7% vs 7%; P = 1.0). The mean clinical follow-up was 24 ± 18 months. TIbE occurred in one patient in each group (P = 1.0). The 3-year freedom from TIbE and freedom from secondary intervention rate was 98% ± 2% and 67% ± 8% for the infrarenal aortic seal group and 97% ± 3% and 67% ± 8% for the iliac seal group, respectively (P = NS). Among the patients treated with infrarenal aortic sealing zones, the mean enlargement of the infrarenal aortic diameter was 5 ± 3.2 mm at 3 years. No late TIbE due to disease progression had developed in the infrarenal aorta. Infrarenal aortic and iliac artery seal zones are safe and effective during FB-EVAR, provided the patients have suitable segments. The use of the infrarenal aortic sealing zone had modest procedural advantages such as shorter endovascular and fluoroscopy times and lower radiation exposure. No differences were found in the clinical outcomes or development of TIbEs. Copyright © 2021 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.