The health care system in the United States is undergoing substantial consolidation through mechanisms ranging from mergers and acquisitions to institutional affiliations to single service agreements, often with expectations of improving the safety and quality of care. However, there has been little evaluation of the risks that system expansion has on patients.1,2 In a partnership between a medical liability insurer (CRICO/Risk Management Foundation) and a health systems research center (Ariadne Labs), we analyzed the patient safety risks for Harvard-affiliated institutions by interviewing clinicians and convening system leaders both locally and nationally. System expansions create 3 types of significant safety risks, often unrecognized and unaddressed, that are related to changes in patient populations, infrastructure, or clinician practice settings (Table).