In 2018, Medicare made participation in the Comprehensive Care for Joint Replacement (CJR) program, which had been mandatory for all hospitals in 67 metropolitan statistical areas (MSAs), voluntary in the 33 of 67 MSAs with the lowest historical costs. CJR was designed to hold hospitals accountable for the cost and quality of care during hip or knee replacement episodes, defined as hospitalization and 90 days of post-discharge care. We compared hospitals that stayed with the CJR program against those that withdrew. This information is important for understanding the effects of voluntary payment models.