OBJECTIVES The objectives were to describe angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor blockers (ARB) use among Medicare Part D enrollees with diabetes and to identify patient characteristics that predict ACEI/ARB utilization. METHODS This is a longitudinal retrospective cohort study. The study sample included Medicare Part D enrollees from 6 states (Alabama, California, Florida, Mississippi, New York, and Ohio) aged 18 years or older with the diagnosis of diabetes. Medicare Part D claims data for the first 6 months of 2006 were evaluated for any utilization of ACEI/ARB. The outcome of interest was the percentage of at least one claim for an ACEI or an ARB during the first half of 2006. RESULTS A total of 1,888,682 patients met our inclusion criteria. Mean age (±SD) was 71.6 (±11.6) years, 59.5% were female, and 66.4% were white. Approximately 58.9%, 5.8%, 0.5% had coexisting hypertension, nephropathy, and hypertension + nephropathy. Overall, 56.9% were receiving ACEI/ARB therapy. Logistic regression indicated that patients with coexisting hypertension + nephropathy and hypertension were 72% and 36% more likely to use ACEI/ARB compared to patients without hypertension and/or nephropathy. However, patients with nephropathy were 24% less likely to receive ACEI/ARB therapy. Females, older patients, and patients of nonwhite races were also more likely to use ACEI/ARB. Patients with myocardial infarction, sleep apnea, coronary artery disease, retinopathy or heart failure were more likely to have used ACEI/ARB, while the opposite was true for those with hypercholesterolemia, peripheral vascular, cerebrovascular, or chronic obstructive pulmonary diseases. All results were statistically significant at P=.0001 level. CONCLUSIONS Less than 60% of Medicare Part D enrollees with diabetes received ACEI/ARB therapy. Several patient characteristics can predict ACEI/ARB use. Opportunities exist for quality-improvement interventions that could increase the outcomes for high-risk patients.