ABSTRACT: Background Cardioprotective medication adherence can mitigate the risk of recurrent cardiovascular events and mortality after acute myocardial infarction ( AMI ). We examined the associations of diabetes mellitus status and glycemic control with cardioprotective medication adherence after AMI . Methods and Results We performed a retrospective observational cohort study of 14 517 US veterans who were hospitalized for their first AMI between 2011 and 2014 and prescribed a beta-blocker, 3-hydroxy-3-methyl-glutaryl-CoA-reductase inhibitor, and angiotensin-converting enzyme inhibitor or angiotensin receptor blocker. The primary exposure was a diagnosis of type 2 diabetes mellitus; in diabetes mellitus patients, hemoglobin A1c (HbA1c) was a secondary exposure. The primary outcome was 1-year adherence to all 3 medication classes, defined as proportion of days covered ?0.8, assessed using adjusted risk differences and multivariable Poisson regression. Of 14 517 patients (mean age, 66.3 years; 98% male), 52% had diabetes mellitus; 9%, 31%, 24%, 15%, and 21% had HbA1c <6%, 6% to 6.9%, 7% to 7.9%, 8% to 8.9%, and ?9%, respectively. Diabetes mellitus patients were more likely to be adherent to all 3 drug classes than those without diabetes mellitus (adjusted difference in adherence, 2.1% [0.5, 3.7]). Relative to those with HbA1c 6% to 6.9%, medication adherence declined with increasing HbA1c (risk ratio of achieving proportion of days covered ?0.8, 0.99 [0.94, 1.04], 0.93 [0.87, 0.99], 0.82 [0.77, 0.88] for HbA1c 7-7.9%, 8-8.9%, and ?9%, respectively). Conclusions Although diabetes mellitus status had a minor positive impact on cardioprotective medication adherence after AMI , glycemic control at the time of AMI may help identify diabetes mellitus patients at risk of medication nonadherence who may benefit from adherence interventions after AMI .