BACKGROUND: Transcatheter aortic-valve implantation (TAVI) is associated with procedure-related stroke. Cerebral embolic protection (CEP) devices may reduce embolization to the cerebral circulation and hence the incidence of stroke. METHODS: We conducted a randomized, controlled trial across 33 centers in the United Kingdom. We randomly assigned 7635 participants with aortic stenosis in a 1:1 ratio to undergo TAVI with a CEP device (CEP group) or TAVI without a CEP device (control group). The primary outcome was stroke within 72 hours after TAVI or before discharge from the hospital (if discharge occurred sooner). RESULTS: A total of 3815 participants were assigned to the CEP group and 3820 to the control group. A primary-outcome event occurred in 81 of 3795 participants (2.1%) in the CEP group and in 82 of 3799 participants (2.2%) in the control group (difference, -0.02 percentage points; 95% confidence interval, -0.68 to 0.63; P = 0.94). Disabling stroke occurred in 47 participants (1.2%) in the CEP group and in 53 (1.4%) in the control group. Death occurred in 29 participants (0.8%) in the CEP group and in 26 (0.7%) in the control group. Overall access-site complications appeared to be similar in the two groups (8.1% in the CEP group and 7.7% in the control group). A total of 24 serious adverse events occurred in 22 of 3798 participants (0.6%) in the CEP group, and 13 serious adverse events occurred in 13 of 3803 participants (0.3%) in the control group. CONCLUSIONS: Among participants undergoing TAVI, routine use of CEP did not decrease the incidence of stroke within 72 hours. (Funded by the British Heart Foundation and Boston Scientific; BHF PROTECT-TAVI ISRCTN Registry number, ISRCTN16665769.).