Abstract Body (Do not enter title and authors here): Background: Thoracic endovascular aortic repair (TEVAR) is the standard treatment for complicated type B aortic dissection, while randomized trials comparing TEVAR and optimal medical therapy for uncomplicated TBAD (uTBAD) are ongoing. Our previous study using a Japanese claims database reported long-term outcomes of uTBAD but did not include individuals aged ≥75 due to the bifurcated insurance system. Objective: To evaluate all-cause mortality associated with TEVAR versus non-TEVAR management in patients with acute uTBAD, including both elderly and non-elderly populations, using real-world data. Methods: We analyzed two national health claim databases, Cohort A (individuals aged ≥75) and Cohort B (self-employed individuals and their family members, all aged <75), from April 2014 to June 2024. Within each cohort, patients with acute uncomplicated type B aortic dissection (uTBAD) were identified using the same criteria. Patients receiving TEVAR during the subacute phase (15–90 days) were assigned to the TEVAR group; others to the non-TEVAR group. Propensity score matching (1:5) was performed separately in each cohort, adjusting for demographics, comorbidities, and medications. All-cause mortality was compared using Kaplan–Meier analysis. Results: After matching, 1,028 patients were included in Cohort A (TEVAR: 174; non-TEVAR: 854) and 730 in Cohort B (TEVAR: 122; non-TEVAR: 608). Median age in Cohort A was 80 (both groups), and in Cohort B was 66.5 (TEVAR) and 67 (non-TEVAR). Median follow-up was 29 vs. 27 months (IQR: 18–40 vs. 17–41) in Cohort A and 35 vs. 32 months (IQR: 19–51 vs. 17–49) in Cohort B for TEVAR and non-TEVAR groups, respectively. Kaplan–Meier analysis showed no significant difference in mortality between groups (log-rank p=0.2205 for A; p=0.2197 for B). Conclusion: In this nationwide real-world study, we observed no statistically significant differences in all-cause mortality between TEVAR and non-TEVAR management within either age cohort. These findings support the clinical equipoise underlying ongoing randomized controlled trials for uTBAD. Meanwhile, patient background and survival outcomes in the non-TEVAR groups within each cohort strongly suggest the influence of age-related confounding factors. Real-world data should be carefully interpreted when used to complement the generalizability of trial findings.