OBJECTIVE: The objective of this study was to evaluate the impact of a multifaceted improvement strategy on diabetes quality of care in a defined population of patients. STUDY DESIGN: A multifaceted improvement strategy to enhance diabetes care was deployed to 18 primary care clinics serving 170,000 adults. Interventions empowered patient self-management, supported care team decision making, redesigned office systems, and maximized use of available information technology. Specific goals were to improve glycemic control and reduce cardiovascular risk in all adult diabetes patients. DATA SOURCE AND COLLECTION: Diabetes was identified through pharmacy and diagnostic data (estimated sensitivity 0.91, positive predictive value 0.94), and the target population ranged from 6,542 to 7,037 members over time. Trends in glycosylated hemoglobin (HbA1c) and low-density lipid LDL-cholesterol were analyzed monthly throughout 1999 in both cohorts and serial cross-sections. RESULTS: During 12 months, mean HbA1c improved from 7.86% to 7.47%, and the proportion of patients with HbA1c levels < 8% rose from 60.5% to 68.3%, and the proportion with HbA1c > 10% fell from 10.3% to 7.2%. The LDL test rate rose from 47.4% to 57.4%, and mean LDL fell from 120 mg/dl to 116 mg/dl. The proportion with acceptable lipid control (LDL < 130 mg/dl, or < 100 mg/dl with coronary artery disease) rose from 48.9% to 57.7%. All changes were significant at p < 0.01 or less. CONCLUSION: Clinically significant population-based improvements in diabetes care were observed during a 1-year period using a multifaceted "enhanced primary care" strategy.