A rigorous evaluation of the effects of continuous quality improvement (CQI) on medical practice has not yet been achieved on a large, multicenter scale. The authors sought to test whether a low-intensity CQI intervention could be used to speed the adoption of two coronary artery bypass grafting process-of-care measures on a national level. The infrastructure of the Society of Thoracic Surgeons' National Cardiac Database was used as a CQI Platform in a prospective randomized trial of CQI conducted between January 2001 and July 2002. Preoperative β-blockade and internal mammary artery grafting in patients aged >75 years were the care processes used. Three hundred fifty-nine National Cardiac Database sites were randomized into two intervention groups (β blocker, n=124; internal mammary artery grafting, n=114) and one control group (n=114). Each intervention arm received measure-specific information, including a call to action to a physician leader; educational products; and periodic longitudinal, nationally benchmarked, site-specific feedback. Incorporation of the specific care process into everyday clinical practice at the intervention site was the main outcome measure. The analyses included a site-level analysis of differences between pre- and postintervention measure use and a hierarchical analysis using risk-adjustment for patient characteristics and accounting for clustering due to site. Use of β blockers increased vs. control (Δ=7% vs. Δ=4%), significant at both the site level (p=0.04) and in the hierarchical analyses (p=0.0006). Internal mammary artery graft use also increased vs. control (Δ=9% vs. Δ=5%; p=0.20 and p=0.11, respectively). However, lower volume IMA sites showed significant improvement over lower volume control sites (Δ=14% vs. Δ=8%; p=0.02 for interaction). A multifaceted, physician-led, low-intensity effort can have an impact on the adoption of care processes into national practice. This Society CQI Platform is a potential model for large-scale quality improvement efforts across all disciplines of medicine.