OBJECTIVES: To study the patterns of discontinuation of ACEI/ARB therapy and to identify factors associated with discontinuation among post myocardial infarction (MI) patients enrolled in Medicare. METHODS: This is a retrospective cohort study utilizing the Medicare 5% national sample claims data for 2006-2007. Medicare beneficiaries with continuous enrollment in Part A, B, and D in 2006-2007, and who were hospitalized for an acute MI between January 1 and June 30 of 2006, were identified using a validated algorithm, requiring a hospitalization episode ≥3 and ≤180 days with an ICD-9-CM of 410.x1 as primary or secondary diagnosis. Post-MI patients with an ACEI/ARB prescription within 90 days of discharge were followed to study patterns of discontinuation until December 31, 2007. Time to discontinuation was defined as the days from initiation of therapy to a therapy gap of >90 days. Survival curves were constructed using the Kaplan-Meier technique, and potential predictors of therapy discontinuation, including demographic characteristics, comorbidities and concomitant medications were estimated using Cox proportional hazards regression. RESULTS: Of the 1,949 subjects in the cohort, 66.1% were females, 82.9% were Caucasian with a mean age of 78.6 (±8.2) years. Approximately, 20% of the patients discontinued therapy within six months and 45% discontinued within a year. Caucasians were less likely to discontinue therapy as compared to blacks (HR=0.774; [0.638-0.939]; p=0.0094). Among the comorbid conditions, dyslipidemia (HR=0.734; [0.612-0.880]; p=0.0008), cerebrovascular disease (HR=1.124; [0.986-1.281]; p=0.0806) and COPD (HR=1.154; [1.013-1.316]; p=0.0319) were significant predictors of time to discontinuation. Patients on concomitant beta-blocker (HR=0.771; [0.627-0.949]; p=0.0141) and statin (HR=0.857; [0.736-0.999]; p=0.0491) therapy were less likely to discontinue ACEI/ARB therapy. CONCLUSIONS: Many patients initiating ACEI/ARB treatment following MI fail to consistently remain on therapy as is evident by the high rates of discontinuation within a year. Several factors including race and comorbidities are potential predictors of this behavior.