To determine if processes and outcomes of diabetes care improved between 2000 and 2006 in a managed care health plan with a comprehensive diabetes disease management program.Cross-sectional.A total of 1650 randomly selected members with diabetes mellitus completed surveys in 2000, and 1256 randomly selected members with diabetes completed surveys in 2006. Survey and medical record data were analyzed using multivariable regression and predictive probabilities adjusted for age, education, and comorbidities.In 2006, patients were more likely to have proteinuria assessed (85% vs 74% in 2000), foot examinations performed (90% vs 86%), glycosylated hemoglobin levels measured (94% vs 87%), lipids measured (81% vs 70%), aspirin use recommended (67% vs 56%), and influenza immunizations administered (70% vs 63%). Glycosylated hemoglobin levels decreased by 0.60% (P <.001), systolic blood pressures by 3 mm Hg (P = .002), and low-density lipoprotein cholesterol levels by 18 mg/dL (P <.001). Those who were continuously enrolled in the health plan were significantly more likely to report having had dilated retinal examinations (P = .003), aspirin use recommendations (P = .049), influenza immunizations (P = .004), and lower low-density lipoprotein cholesterol levels (by 6 mg/dL, P = .003).Implementation of a disease management program was associated with substantial improvements in processes and outcomes of diabetes care over 6 years. Although secular trend likely contributed somewhat, improvement in other measures was significantly associated with duration of enrollment in the health plan, making secular trend an unlikely explanation for all of our findings.