Sex-based differences exist in the prevalence and clinical presentation of abdominal aortic aneurysm (AAA). However, it is unclear if sex is associated with AAA repair type and long-term mortality. To investigate whether a sex-related difference exists in mortality risk after AAA repair owing to differences in repair type. This cohort study uses data from the Vascular Quality Initiative, a national clinical registry, and Medicare claims to investigate endovascular and surgical repair procedures performed between January 1, 2003, and September 30, 2015, in patients aged 65 years or older with AAA. The data were analyzed from October 1, 2018, to November 19, 2019. Sex of the patient. Endovascular (EVR) or open surgical AAA repair type and subsequent long-term, all-cause mortality. In this cohort study of 16 386 patients, 12 757 (77.9%) were men and 3629 (22.1%) were women. Women were more likely than men to be older (mean [SD] age, 77 [6.5] years vs 75 [6.6] years; P < .001), active smokers (33% vs 28%; P < .001), and to have smaller aneurysms (mean [SD] diameter, 57 [11.7] mm vs 59 [17.7] mm; P < .001). Surgical AAA repair was performed in 27% (983 of 3629) of women compared with 18% (2328 of 12 757) of men (P < .001). After inverse probability weighting for risk adjustment, women were more likely to receive open surgical repair than EVR repair (risk ratio, 1.65; 95% CI, 1.51-1.80). The 10-year unadjusted survival rate after EVR repair was 14% lower in women than in men (23% vs 37%; log-rank P < .001), but the rates were comparable after open surgical repair (36% in men vs 32% in women; log-rank P = .22). Risk-adjusted analysis showed that women were associated with higher mortality rates after EVR repair (hazard ratio, 1.13; 95% CI, 1.03-1.24), whereas both men and women had a similar risk of death after open surgical repair (hazard ratio, 0.94; 95% CI, 0.84-1.06). After further stratification by symptom severity, higher risk of mortality among women was limited to elective EVR and open surgical repair for ruptured AAA. In this study, women were 65% more likely than men to undergo open surgical repair. After EVR repair, women were 13% more likely to die than men, although no sex-based difference in mortality was found after open surgical repair. The differential treatment benefit of EVR repair in women is concerning given the shift toward an EVR-first approach to AAA repair.