Medicare's new hospital pay-for-performance program for all acute care hospitals will begin in October 2012. It will be the largest Medicare quality improvement initiative for hospitals to date. Using 2009 data on hospital performance, we calculated hospital performance scores and projected payments under the new program for all eligible hospitals. Despite differences across hospitals in terms of performance, expected changes in payments were small, even for hospitals with the best and worst performance scores. Almost two-thirds of hospitals would experience changes of just a fraction of 1 percent. Although the program will in effect redistribute resources among hospitals, our data suggest that the redistribution is not likely to cause major problems because the amount being redistributed is also small. These results raise questions about whether the new pay-for-performance program will substantially alter the quality of hospital care, and they highlight the challenges of designing effective quality improvement incentives.