OBJECTIVES: ACEI or ARB therapy in patients with diabetes has been shown to delay progression to renal failure.  This study evaluated the impact of a mailing intervention to healthcare providers aimed at optimizing ACEI or ARB therapy in patients with diabetes plus hypertension and/or nephropathy.   METHODS: A retrospective cohort study was performed using pharmacy claims data from a large Medicare Part D plan to evaluate an intervention notifying providers of missing ACEI/ARB therapy for 28,348 patients with diabetes plus hypertension and/or nephropathy not qualifying for Medication Therapy Management services (Non-MTM).  A control cohort of 50,757 Non-MTM Medicare Part D patients with diabetes plus hypertension and/or nephropathy not receiving ACEI or ARB therapy during the 7-month identification period was selected from an earlier timeframe to be compared to the intervention cohort.  The primary outcome was the percentage of identified patients initiating ACEI or ARB therapy during the 4-month post-intervention period. Logistic regression was performed using a dependent variable of initiation vs. no initiation of ACEI or ARB therapy in the post-intervention period. Independent variables included age, gender, chronic disease score, and hypertension and nephropathy diagnoses. RESULTS: During the post-intervention period, the unadjusted proportion of those beginning ACEI or ARB therapy was 15.0% for the intervention group compared to 12.2% for the control group (p <0.0001).  After adjusting for baseline characteristics, intervened patients had greater odds of initiating ACEI or ARB therapy compared to control patients (OR 1.40; 95% CI 1.33 – 1.48).  A limitation of the evaluation is that the identification and measurement periods for the control group were in a different part of the year than the intervention cohort.  CONCLUSIONS: Intervention in patients with diabetes plus hypertension and/or nephropathy via healthcare providers demonstrated an increased likelihood of initiation of ACEI or ARB therapy compared to a control group.