The purpose of this study was to document trends in diabetes quality of care and coinciding strategies for quality improvement over 10 years in a large medical group. Adults with diagnosed diabetes mellitus were identified each year from 1994 (N = 5610) to 2003 (N = 7650), and internal medical group data quantified improvement trends. Multivariate analysis was used to identify factors that did and did not contribute to improvement trends. Median glycosylated hemoglobin A1C (A1C) levels improved from 8.3% in 1994 to 6.9% in 2003 (P <.001). Mean low-density lipoprotein (LDL) cholesterol measurements improved from 132 mg/dL in 1995 to 97 mg/dL in 2003 (P <.001). Both A1C (P <.01) and LDL improvement (P <.0001) were driven by drug intensification, leadership commitment to diabetes improvement, greater continuity of primary care, participation in local and national diabetes care improvement initiatives, and allocation of multidisciplinary resources at the clinic level to improve diabetes care. Resources were spent on nurse and dietitian educators, active outreach to high-risk patients facilitated by registries, physician opinion leader activities including clinic-based training programs, and financial incentives to primary care clinics. Use of endocrinology referrals was stable throughout the period at about 10% of patients per year, and there were no disease management contracts to outside vendors over the study period. Electronic medical records did not favorably affect glycemic control or lipid control in this setting. This primary care-based system achieved A1C and LDL reductions sufficient to reduce macrovascular and microvascular risk by about 50% according to landmark studies; further risk reduction should be attainable through better blood pressure control. Strategies for diabetes improvement need to be customized to address documented gaps in quality of care, provider prescribing behaviors, and patient characteristics.