Context: Efforts to improve quality of care in the cardiac surgery field have focused on reducing the risk-adjusted mortality associated with common surgical procedures, such as coronary artery bypass grafting (CABG). However, the best methodological approach to improvement is under debate. Objective: To test an intervention to improve performance of CABG surgery. Design and Setting: Quality improvement project based on baseline (July 1, 1995-June 30, 1996) and follow-up (July 1-December 31, 1998) performance measurements from medical record review for all 20 Alabama hospitals that provided CABG surgery. Patients: Medicare patients discharged after CABG surgery in Alabama (n=5784), a comparison state (n=3214), and a national sample (n=3758). Intervention: Confidential hospital-specific performance feedback and assistance with multimodal improvement interventions, including the option to share relevant experience with peers. Main Outcome Measures: Duration of intubation, reintubation rate, aspirin therapy at discharge, use of the internal mammary artery (IMA), hospital readmission rate, and risk-adjusted in-hospital mortality. Results: Proportion of extubation within 6 hours increased from 9% to 41% in Alabama, decreased from 40% to 39% in the comparison state, and increased from 12% to 25% in the national sample. Use of IMA increased from 73% to 84%, 48% to 55%, and 74% to 81%, respectively, in the 3 samples, but aspirin use increased only in Alabama (from 88% to 92%). The amount of improvement in all 3 of these process measures was greater in Alabama than in the other samples (IMA use for Alabama vs comparison state was P=.001 and for Alabama vs national sample; P=.02; and P<.001 for all other comparisons). Risk-adjusted mortality decreased in Alabama (4.9% to 2.9%), but this decrease was not statistically significantly different from mortality changes in the other groups (odds ratio, 0.76; 95% confidence interval, 0.54-1.07 vs national sample). Conclusion: Confidential peer-based regional performance feedback and process-oriented analysis of shared experience are associated with some improvement in quality of care for patients who underwent CABG surgery.