BACKGROUND: Hospitals are under increasing pressure to measure and improve quality of care, and substantial resources are being directed at a variety of quality improvement strategies; however, the evidence base supporting these strategies is limited. OBJECTIVE: We sought to identify quality improvement efforts that were associated with hospitals' beta-blocker prescription rates after acute myocardial infarction (AMI). RESEARCH DESIGN: This was a cross-sectional study using data from a telephone survey of quality management directors at participating hospitals linked with patient-level data from the National Registry of Myocardial Infarction (NRMI) during the study period, October 1997 to September 1999. SUBJECTS: A total of 60,363 patients discharged with a confirmed AMI from 234 US hospitals were included. MEASURES: Hospital performance based on beta-blocker rates characterized as the top 20%, lower 20%, and middle 40% of hospitals; reported quality improvement efforts, including system interventions, physician leadership, administrative support for quality improvement efforts, and data feedback; hospital teaching status, AMI volume, geographic location, and ownership type. RESULTS: The mean hospital-specific beta-blocker rate was 60.2%; however, the variation in beta-blocker use across hospitals was marked (range, 19.4-89.3%, standard deviation, 12.7% points), and quality improvement efforts used varied greatly. None of the quality improvement efforts distinguished higher from medium performers; the higher and the medium performers together were distinguished from the lower performers in organizational support for quality improvement efforts (fully adjusted odds ratio [OR] 1.89, 95% confidence interval [CI] 1.17-3.06) and physician leadership (fully adjusted OR 9.88, 95% CI 2.64-37.02). Among the specific quality improvement interventions, only standing orders were associated with having higher/medium versus lower performance, and their effect had borderline significance (fully adjusted OR 2.26, 95% CI 0.97-5.30, P = 0.07). CONCLUSIONS: Our findings highlight the organizational environment, specifically the absence of administrative support or physician leadership for quality improvement, as an important correlate of poor beta-blocker rates after AMI. Future studies are needed to isolate hospital quality improvement efforts that are associated with superior performance.