OBJECTIVE: To evaluate the impact of a population-based, diabetes intervention program on patient self-management behaviors and health system screening practices and risk factor management. METHODS: A population-based diabetes intervention program was developed by a large, regional managed care plan in the northern Midwest and a health management subsidiary of a pharmaceutical company. Program interventions included periodic education mailings, brochures, newsletters and kits, as well as telephonic case management for high-risk patients. Six hundred thirty-eight diabetic members of the health plan completed surveys before and after one year of program participation, with a 48% response rate. A second cohort of 956 diabetic patients that did not participate in the interventions served as a control group. The evaluation of program impact was examined using two quasi-experimental designs: 1) one-group pretest-posttest, and 2) a posttest only design with nonequivalent groups. Information solicited in the survey included quality of life issues, frequency of monitoring activities, behavioral risk factor management, and intermediate clinical outcomes (i.e., HbA1c values, blood pressure, blood glucose levels). RESULTS: Mean quality of life scores (PAID) improved significantly from baseline in the intervention group (P<.01) and were significantly higher than controls (P<.01). Statistical improvements (P<.01)were noted from baseline for blood glucose monitoring. At follow-up, significantly more patients in Cohort 1 reported pre-meal blood glucose levels of <140 (P<.01) and mean decreases in low and high blood sugar episodes. Clinical screening exams were almost all significantly improved in the intervention group compared with controls. With the exception of smoking, which showed a significant decrease in the intervention group, health behaviors such as following a meal plan and exercising were not affected. There were no changes reported in body mass index (BMI). CONCLUSIONS: A population-based intervention program implemented within a large health plan produced measurable improvements in diabetes-related behaviors and outcomes.