BackgroundWe sought to define surgical outcomes among elderly patients with Alzheimer's disease and related dementias (ADRD) following major thoracic and gastrointestinal surgery.MethodsA retrospective cohort study was used to identify patients who underwent coronary artery bypass grafting (CABG), abdominal aortic aneurysm (AAA) repair, pneumonectomy, pancreatectomy, and colectomy. Individuals were identified from the Medicare Standard Analytic Files and multivariable regression was utilized to assess the association of ADRD with textbook outcome (TO), expenditures, and discharge disposition.ResultsAmong 1,175,010 Medicare beneficiaries, 19,406 (1.7%) patients had a preoperative diagnosis of ADRD (CABG: n = 1,643, 8.5%; AAA repair: n = 5,926, 30.5%; pneumonectomy: n = 590, 3.0%; pancreatectomy: n = 181, 0.9%; and colectomy: n = 11,066, 57.0%). After propensity score matching, patients with ADRD were less likely to achieve a TO (ADRD: 31.2% vs. no ADRD: 40.1%) or be discharged to home (ADRD: 26.7% vs. no ADRD: 46.2%) versus patients who did not have ADRD (both p < 0.001). Median index surgery expenditures were higher among patients with ADRD (ADRD: $28,815 [IQR $14,333–$39,273] vs. no ADRD: $27,101 [IQR $13,433–$38,578]; p < 0.001) (p < 0.001). On multivariable analysis, patients with ADRD had higher odds of postoperative complications (OR 1.32, 95% CI 1.25–1.40), extended length‐of‐stay (OR 1.26, 95% CI 1.21–1.32), 90‐day readmission (OR 1.37, 95% CI 1.31–1.43), and 90‐day mortality (OR 1.76, 95% CI 1.66–1.86) (all p < 0.001).ConclusionPreoperative diagnosis of ADRD was an independent risk factor for poor postoperative outcomes, discharge to non‐home settings, as well as higher healthcare expenditures. These data should serve to inform discussions and decision‐making about surgery among the growing number of older patients with cognitive deficits.