BACKGROUND: During 2000-03, Qualidigm, a US Quality Improvement Organization, conducted a project to improve the care received by elderly Medicare patients with coronary artery disease or cardiovascular risk factors. METHODS: We recruited primary care physicians in private practice in the state of Connecticut. Then, we identified approximately 30-50 patients per physician from the periods 1 January 2000 to 31 December 2000 and 1 November 2001 to 31 October 2002. We abstracted medical records to assess processes and outcomes of care, and we provided the physicians with performance data and a variety of practice-enhancing materials. The physicians utilized those materials that they perceived to be most helpful. RESULTS: We identified and recruited 974 primary care physicians to participate. Of these, 103 (10.6%) committed to participate, and 85 of the 103 completed the project. Among the intervention tools, physicians and their office personnel utilized personal digital assistants (PDAs) (36.5%) and patient education materials (34.1%) most commonly. Overall, quality of care improved for most physicians (mean quality score 62.0 to 67.8%, P < 0.001). However, not all improved, and most improvements were modest [mean absolute improvement in quality score 5.8%, standard deviation (SD) 6.8%]. CONCLUSIONS: Quality Improvement Organizations and others interested in improving outpatient quality of care face significant challenges in recruiting self-employed primary care physicians to quality improvement projects and in bringing about transformational change. Future primary care quality improvement projects should include careful assessments of practice-specific barriers, interventions that are linked to these barriers, and support of the practices on implementation.