Background: Frailty is associated with a higher risk for adverse outcomes after aortic valve replacement (AVR) for severe aortic valve stenosis, but whether or not frail patients derive differential benefit from transcatheter (TAVR) vs. surgical (SAVR) AVR is uncertain. Methods: We linked adults ≥ 65 years old in the US CoreValve High Risk (HiR) or Surgical or Transcatheter Aortic-Valve Replacement in Intermediate Risk Patients (SURTAVI) trial to Medicare claims, 2/2/2011-9/30/2015. Two frailty measures, a deficit-based (DFI) and phenotype-based (PFI) frailty index, were generated. The treatment effect of TAVR vs. SAVR was evaluated within frailty index (FI) tertiles for the primary endpoint of death and non-death secondary outcomes, using multivariable Cox regression. Results: Of 1,442 (linkage rate = 60.0%) individuals included, 741 (51.4%) individuals received TAVR and 701 (48.6%) received SAVR (mean age 81.8 ± 6.1 years, 44.0% female). Though 1-year death rates in the highest FI tertiles (DFI 36.7%, PFI 33.8%) were 2-3-fold higher than the lowest tertiles (DFI 13.4%, HR 3.02, 95% CI 2.26-4.02, p < 0.001; PFI 17.9%; HR 2.05, 95% CI 1.58-2.67, p < 0.001), there were no significant differences in the relative or absolute treatment effect of SAVR vs. TAVR across FI tertiles for all death, non-death, and functional outcomes (all interaction p-values > 0.05). Results remained consistent across individual trials, frailty definitions, and when considering the non-linked trial data. Conclusions: Two different frailty indices based on Fried and Rockwood definitions identified individuals at higher risk of death and functional impairment but no differential benefit from TAVR vs. SAVR.