This paper examines the impact that Medicare pay-for-performance (P4P) might have upon hospital payment. It uses the initial two quarters of a national quality database to model financial gains or losses using the Premier Hospital Quality Incentive Demonstration rules, as well as the P4P approach recommended by the Medicare Payment Advisory Commission (MedPAC). Findings reveal variation among all types of hospitals and across all measures within each of the three conditions studied: heart attack, heart failure, and pneumonia. Initially, hospitals' financial gains and losses likely will be marginal using the Premier demonstration payment rules and somewhat larger under the MedPAC recommendations as modeled.