Endovascular repair of complex abdominal (CAAA) and thoracoabdominal aortic aneurysms (TAAA) with fenestrated and branched devices (F/BEVAR) represents the first-line treatment in old or unfit patients. Currently, the widespread diffusion of these techniques has led to a progressive increase of complex endovascular procedures also in younger and fitter patients, but the related results have been only minimally reported without long-term data. We investigated the long-term results of F/BEVAR for CAAA and TAAA repair in young and fit patients. All consecutive patients, aged 70 or younger, undergone F/BEVAR for CAAA and TAAA over the last 13 years at two tertiary Institutions were included in the study. All subjects presented a low to intermediate risk according to the Society for Vascular Surgery (SVS) clinical comorbidity grading system. The primary endpoints were technical and clinical success, late overall and aortic-related survival. Major complications and specific target vessel-related outcomes were investigated as secondary endpoints. A total of 183 patients (155 males, 84.7%; mean age 64.5 + 5.7 years, range 33-70) underwent F/BEVAR during the study period, for a total of 167 (91.3%) degenerative and 16 (8.7%) post-dissection aneurysms including 44 (24%) juxtarenal, 33 (18%) pararenal and 106 (58%) thoraco-abdominal aortic aneurysms. Technical and clinical success were achieved in 176 (96.2%) and 171 patients (93.4%), respectively. Four patients (2.2%) died perioperatively, of which 2 (1.1%) operated in emergency. Postoperatively, 5 patients (2.7%) presented permanent grade 3 spinal cord injury, and 3 (1.6%) renal failure needing permanent dialysis. The mean follow-up was 65.7 + 39.6 months (range 1-158). Estimated overall and aortic-related survival at 12, 60, and 120 months was 94.0%, 85.1%, 72.2%, and 97.8%, 97.8%, 96.2%, respectively, while reintervention and branch instability-free survival at the same time spam was 84.4%, 71.8%, 71.8%, and 93.2%, 86.3%, 72.2%, respectively. An aneurysm growth > 5 mm was detected in 6 patients (3.3%) while a sac shrinkage > 5 mm was achieved in 118 cases (64.5%). The Cox regression analysis demonstrated the need for unplanned procedure as the only risk factor for overall mortality [OR=3.331 (1.397-7.940), p < 0.01]. F/BEVAR in young and fit patients led to a low perioperative mortality and major morbidity, and favorable overall survival rate in the long-term making this technique particularly appealing in such a subgroup of patients. The availability of long-term data derived from the results of young patients, may additionally provide helpful information to re-define indication for treatment and allow future targeted device and technique improvements.