The American Board of Internal Medicine’s Maintenance of Certification program includes an assessment of physicians’ efforts to improve the quality of their patient care through a web-based reporting system called the Practice Improvement Modules. Data collected from the Comprehensive Care (CC) PIM, includes 192 primary care practice system questionnaires, 5,676 patient surveys, and 18,473 chart audits. Systems questionnaires were used in a K-means cluster analysis to identify two types of office practices: those using Evidence-based care versus other systems of ambulatory care. Mixed linear models were used for estimating practice level means of clinical outcomes and patient ratings adjusted for patient factors and for tests of differences between practice types. The hypothesis that Evidence-based practices have better outcomes than other practice types was partially supported.