In this study, Neprash and colleagues estimated the association between changes in physician-hospital integration in metropolitan statistical areas from 2008 to 2012 and concurrent changes in commercial health care spending and prices, adjusting for patient, plan, and market characteristics, including physician, hospital, and insurer market concentration. Neprash and colleagues found physician-hospital integration increased by a mean 3.3 percentage points. An increase in outpatient spending was driven almost entirely by price increases, as associated changes in use were minimal. Changes in physician-hospital integration were not associated with significant changes in inpatient spending or use. These findings are consistent with hospitals and hospital systems conferring their market power on newly employed physicians and acquired practices as the integrated organization negotiates prices for outpatient physician services. To the extent that payment reforms accelerate physician-hospital integration, commercial health care prices may rise as an unintended consequence.