The share of patients with kidney failure enrolled in Medicare Advantage (MA) increased from 27 percent to 47 percent after the implementation of the 21st Century Cures Act, which expanded MA eligibility to all kidney failure patients. In this mixed-methods study, we examined the characteristics of dialysis facilities participating in MA contracts in 2021, and we supplemented the findings with data from qualitative interviews with representatives from MA plans and dialysis provider organizations. In 2021, dialysis facilities contracted with approximately 60 percent of MA plans offered in their and neighboring counties. In adjusted analyses, facilities affiliated with the two large dialysis organizations had 33-40 percentage points higher participation in MA networks compared with independent, not-for-profit facilities. Interviews suggest that large dialysis organizations had a unique advantage in their negotiations with MA plans. It is important for policy makers to understand how MA enrollment growth among people with kidney failure may be accelerating consolidation in the dialysis market.