Ambulatory surgical centers (ASCs) are increasingly being acquired by private equity firms, yet the implications for patients remain understudied. In this study we employed a quasi-experimental difference-in-differences design within an event study framework to assess changes in outcomes associated with the acquisition of ASCs by private equity entities. Using a two-way fixed effects model, we assessed the baseline probability of an unplanned hospital visit, total costs, and total encounters three years preacquisition compared with three years postacquisition in ASCs acquired by private equity versus those acquired by non-private equity entities. We identified ninety-one ASCs acquired by private equity and fifty-seven ASCs acquired by non-private equity entities during the period 2011-14. There was no statistically significant observed change in the probability of an unplanned hospital visit, total costs, or total encounters after acquisition by private equity relative to acquisition by non-private equity entities. When we compared private equity-acquired ASCs with matched ASCs that were never acquired, we also found no statistically significant relative change in the probability of an unplanned hospital visit, total costs, or total encounters. Regulators should ensure that data on private equity acquisitions are transparent and that data are available to track the long-term quality and financial implications of these acquisitions.