Medicare Accountable Care Organizations (ACOs) with longer participation in the Medicare Shared Savings Program (MSSP) during 2013 through 2015 had a greater likelihood of reducing their costs and meeting the shared savings benchmarks. About 46% of ACOs that participated for one year were able to reduce spending. However, among ACOs that participated continuously from 2013 through 2015, 57% were able to reduce spending, and by greater amounts. The 46% of ACOs that were in the program for one year reduced spending by $5.4 million for that year. The ACOs that participated for all three years reduced spending by an . . .