BACKGROUND: Endovascular aneurysm repair (EVAR) has become increasingly prevalent for treating asymptomatic abdominal aortic aneurysms (AAAs). This study compares the early and late outcomes between EVAR and open aneurysm repair (OAR) in asymptomatic AAA patients. METHODS: A retrospective observational cohort study was conducted involving 564 patients (445 EVAR and 119 OAR) who underwent AAA repair from January 2010 to January 2022. Primary outcomes included 30-day and in-hospital mortality. Secondary outcomes encompassed operative details, hospital stay, complications, and long-term survival. A post-hoc noninferiority analysis for 30-day mortality was performed with a noninferiority margin of 1%. RESULTS: EVAR patients were older (75.6 ± 7.7 vs. 68.7 ± 9.5 years, P <
0.001) and more often deemed unfit for open repair (53.0% vs. 10.1%, P <
0.001). EVAR demonstrated advantages in operative time (149.5 ± 70.8 vs. 303.5 ± 115.7 minutes, P <
0.001), blood loss (median 200 vs. 1,500 mL, P <
0.001), and hospital stay (median 5 vs. 9 days, P <
0.001). Thirty-day mortality was 0.9% for EVAR and 3.4% for OAR. Post-hoc noninferiority analysis suggested EVAR was noninferior to OAR for 30-day mortality (difference -2.47%, 95% confidence interval: -0.5% to 5.4%, P = 0.005). EVAR had significantly fewer early reinterventions (1.3% vs. 8.4%, P <
0.001). Detailed complication analysis revealed that EVAR had significantly fewer early laparotomy-related complications (0.2% vs. 5.0%, P <
0.001) but more late aneurysm-related complications (16.9% vs. 5.0%, P = 0.002). Conversely, OAR had more late laparotomy-related complications (8.4% vs. 0.2%, P <
0.0001). The combined rate of late complications was not significantly different between groups (17.1% vs. 13.4%, P = 0.314). The EVAR group exhibited lower 5-year survival, likely due to the higher proportion of elderly and unfit patients. CONCLUSIONS: The post-hoc noninferiority analysis suggests that EVAR is noninferior to OAR in terms of 30-day mortality for asymptomatic AAA patients. EVAR demonstrated perioperative benefits and fewer early complications, while long-term complication profiles differed between procedures. These findings support EVAR as a valuable option, particularly for higher-risk patients, while highlighting the need for procedure-specific long-term surveillance. Future prospective studies are needed to confirm these post-hoc findings.