To evaluate the effect of frailty assessed by the modified Frailty Index (mFI) on major adverse cardiac and cerebrovascular events (MACCE) in the elderly patients after endovascular aortic aneurysm repair (EVAR). This was a retrospective cohort study of elderly patients who underwent EVAR in a tertiary hospital. The main exposure was frailty status assessed by the mFI. The primary outcomes were 30-day and long-term MACCE. The predictive ability of the mFI was compared with the Revised Cardiac Risk Index (RCRI) using net reclassification improvement (NRI) and integrated discrimination improvement (IDI) statistics. Of 749 participants, 134 (17.89%) were identified as frail and 185 (24.70%) as prefrail. Thirteen patients (1.74%) were lost in follow-up after surgery, and the median length of follow-up was 32.00 months (range, 15.00-59.25 months). Frailty was associated with a significantly increased risk of 30-day MACCE (adjusted odds ratio OR, 14.53; 95% confidence interval [CI], 4.59-46.04; P < .0001) and longer intensive care unit stay (adjusted odds ratio, 2.43; 95% CI, 1.17-5.07; P = .0176). As for long-term outcomes, both frailty and prefrailty were associated significantly increased risks of MACCE after EVAR (prefrail: adjusted hazard ratio [HR] 1.71; 95% CI, 1.12-2.61; frail: adjusted HR, 3.37; 95% CI, 1.86-6.10). When considering death as a competing risk, we also observed a significant association between frailty and cardiac and cerebrovascular events (adjusted HR, 2.95; 95% CI, 1.06-8.15). In addition, frailty was associated with a significantly increased risk of all-cause mortality (adjusted HR, 1.93; 95% CI, 1.28-2.90). Compared with the RCRI, the mFI had better discrimination in predicting 30-day MACCE (IDI: 0.225; 95% CI, 0.018-0.431; P = .033; NRI: 0.225; 95% CI, 0.023-0.427; P = .029) and long-term MACCE (IDI: 0.056; 95% CI, 0.018-0.128; P = .013; NRI: 0.237; 95% CI, 0.136-0.359; P < .001). Frailty assessed by the mFI may serve as a useful predictor of both short-term and long-term MACCE in elderly patients after EVAR, with improved discrimination and reclassification abilities compared with the RCRI. Copyright © 2021 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.