A rollup is a series of acquisitions through which a financial sponsor consolidates ownership. Increasingly, this strategy is shaping economically important markets, but historically, it has escaped antitrust enforcement. We study this phenomenon in the anesthesia industry, home to the first rollup-based antitrust case in US history. Using procedure-level claims data, we study the litigated transactions, identify eighteen other observationally similar rollups, and document their effects on market structure. We then show prices rise sharply as competing practices are acquired. Finally, we estimate a structural bargaining model and simulate counterfactual equilibrium outcomes under remedies that courts are likely to consider.