This study examined changes in the risk-adjusted mortality associated with coronary artery bypass grafting procedures performed in New York State during the first 4 years of New York's Cardiac Surgery Reporting System (1989 to 1992). To track performance over time, surgeons and hospitals were subdivided into three groups on the basis of their performance in 1989. The risk-adjusted mortality for each of the three groups was computed for 1992 and compared with their 1989 mortality. The results indicate that all groups of providers exhibited large reductions in the risk-adjusted mortalities, with the groups that showed the highest initial mortalities manifesting the most improvement. However, the group rankings remained the same in 1992 as they were in 1989. For example, when the hospital groups were based on the terciles of risk-adjusted mortality observed in 1989, the risk-adjusted mortality decreased from 2.72% to 2.19% for group 1, from 4.24% to 2.51% for group 2, and from 7.12% to 2.77% for group 3. Notably, the risk-adjusted mortalities of the three groups were all significantly different from one another in 1989, but were not significantly different from one another in 1992. Another interesting finding was that the volume of operations performed by the various provider groups did not change substantially in the 4-year period.