Concentration in the U.S. health care sector has been on the rise over the past two decades. Starting with horizontal consolidation, it has spread to vertical mergers and acquisitions and megamergers of national players at multiple levels of the supply chain. Given the financial difficulty that many providers have suffered during the pandemic, this trend is likely to continue, reducing competition and increasing prices. In light of this danger, Congress and regulators should take steps now to more fully assess the impact and curb those combinations that adversely impact payers and patients.