Thoracic endovascular aortic repair (TEVAR) results have been studied in short-term time frames. This study aimed to evaluate midterm and long-term outcomes of TEVAR, emphasizing postoperative aortic remodeling and need for reintervention. This is an institutional retrospective review of TEVAR for isolated descending thoracic aortic aneurysms. Data were collected from 2004 to 2018. Primary outcomes studied included aneurysm sac remodeling, freedom from reintervention, and all-cause mortality. Other outcomes studied include endoleak rates, neurologic complication rates, and any overall postoperative complication rates. During the study period, 219 patients underwent TEVAR for descending thoracic aortic aneurysms. The median effect of TEVAR on sac diameter was a 0.7-cm decrease in size (interquartile range, -1.4 to 0.0 cm). During the study period, 80% (n = 147) of patients experienced aneurysm sac regression or stability. Perioperative neurologic complications occurred in 16% (n = 34) of patients. Significant predictors of sac growth were endoleak (odds ratio [OR], 65; P < .001), preoperative carotid-subclavian bypass (OR, 8; P = .003), and graft oversizing <20% (OR, 15; P = .046). Every 1-mm increase in aortic diameter at the proximal TEVAR landing zone led to an increased odds of endoleak (OR, 2; P = .049). Access complications (OR, 8) and subclavian artery coverage (OR, 6) significantly increased the odds of reintervention, whereas every percentage of graft oversizing protected against reintervention (OR, 0.005). Life-table analysis revealed an overall survival of 78% (71%-83%) at median follow-up. At 3 years, survival was 88% (80%-93%) for those with aneurysm sac stability or regression, whereas it was 70% (49%-84%) for those with aneurysm sac growth (P = .0402). Cox proportional hazards model showed that the only protective factor for mortality was percentage oversizing, with every 1% of oversizing having a hazard ratio (HR) of <.001 (P = .032). This was counterbalanced by the fact that patients with graft oversizing >30% had an increased odds of mortality with HR >10 (P = .049). Other significant factors that increased the odds of mortality included endoleak (HR, 3.6; P = .033), diabetes (HR, 4.1; P = .048), age (every 1-year increase in age; HR, 1.2; P = .002), year of surgery (every year subsequent to 2004; HR, 1.3; P = .012), and peripheral artery disease (HR, 5.2; P = .041). The majority of patients (80%) experience sac stability or regression after TEVAR, which offers a clear survival advantage. Endoleaks are predictive of sac growth, conferring increased mortality. Rigorous surveillance is necessary to prevent future aortic events through reintervention.