Transcatheter aortic valve replacement (TAVR) may be associated with less delirium and allow faster recovery than surgical aortic valve replacement (SAVR). To examine the association of delirium and its severity with clinical and functional outcomes after SAVR and TAVR. Prospective cohort study. An academic medical center. A total of 187 patients, aged 70 years and older, undergoing SAVR (N = 77) and TAVR (N = 110) in 2014 to 2016. Delirium was assessed daily using the Confusion Assessment Method (CAM), with severity measured by the CAM-Severity (CAM-S) score (range = 0-19). Outcomes were prolonged hospitalization (9 days or more); institutional discharge; and functional status, measured by ability to perform 22 daily activities and physical tasks over 12 months. SAVR patients had a higher incidence of delirium than TAVR patients (50.7% vs 25.5%; P < .001), despite younger mean age (77.9 vs 83.7 years) and higher baseline Mini-Mental State Examination score (26.9 vs 24.7). SAVR patients with delirium had a shorter duration (2.2 vs 3.4 days; P = .04) with a lower mean CAM-S score (4.5 vs 5.7; P = .01) than TAVR patients with delirium. The risk of prolonged hospitalization in no, mild, and severe delirium was 18.4%, 30.8%, and 61.5% after SAVR (P for trend = .009) and 26.8%, 38.5%, and 73.3% after TAVR (P for trend = .001), respectively. The risk of institutional discharge was 42.1%, 58.3%, and 84.6% after SAVR (P for trend = .01) and 32.5%, 69.2%, and 80.0% after TAVR (P for trend <.001), respectively. Severe delirium was associated with delayed functional recovery after SAVR and persistent functional impairment after TAVR at 12 months. Less invasive TAVR was associated with lower incidence of delirium than SAVR. Once delirium developed, TAVR patients had more severe delirium and worse functional status trajectory than SAVR patients did. NCT01845207. © 2019 The American Geriatrics Society.