BACKGROUND: Surgical risk scores do not include frailty assessments (eg, gait speed), which are of particular importance for patients with severe aortic stenosis considering transcatheter aortic valve replacement. METHODS AND RESULTS: We assessed the association of 5-m gait speed with outcomes in a cohort of 8039 patients who underwent transcatheter aortic valve replacement (November 2011-June 2014) and were included in the Society of Thoracic Surgeons/American College of Cardiology Transcatheter Valve Therapy Registry. We evaluated the association between continuous and categorical gait speed and 30-day all-cause mortality before and after adjustment for Society of Thoracic Surgeons-predicted risk of mortality score and key variables. Secondary outcomes included in-hospital mortality, bleeding, acute kidney injury, and stroke. The overall median gait speed was 0.63 m/s (25th-75th percentile, 0.47-0.79 m/s), with the slowest walkers (<0.5 m/s) constituting 28%, slow walkers (0.5-0.83 m/s) making up 48%, and normal walkers (>0.83 m/s) constituting 24% of the population. Thirty-day all-cause mortality rates were 8.4%, 6.6%, and 5.4% for the slowest, slow, and normal walkers, respectively (P<0.001). Each 0.2-m/s decrease in gait speed corresponded to an 11% increase in 30-day mortality (adjusted odds ratio, 1.11; 95% confidence interval, 1.01-1.22). The slowest walkers had 35% higher 30-day mortality than normal walkers (adjusted odds ratio, 1.35; 95% confidence interval, 1.01-1.80), significantly longer hospital stays, and a lower probability of being discharged to home. CONCLUSIONS: Gait speed is independently associated with 30-day mortality after transcatheter aortic valve replacement. Identification of frail patients with the slowest gait speeds facilitates preprocedural evaluation and anticipation of a higher level of postprocedural care. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01737528.