Importance: High-intensity statins are recommended following myocardial infarction. However, patients may not continue taking this medication with high adherence. Objective: To estimate the proportion of patients filling high-intensity statin prescriptions following myocardial infarction who continue taking this medication with high adherence and to analyze factors associated with continuing a high-intensity statin with high adherence after myocardial infarction. Design, Setting, and Participants: Retrospective cohort study of Medicare patients following hospitalization for myocardial infarction. Medicare beneficiaries aged 66 to 75 years (n = 29 932) and older than 75 years (n = 27 956) hospitalized for myocardial infarction between 2007 and 2012 who filled a high-intensity statin prescription (atorvastatin, 40-80 mg, and rosuvastatin, 20-40 mg) within 30 days of discharge. Beneficiaries had Medicare fee-for-service coverage including pharmacy benefits. Exposures: Sociodemographic, dual Medicare/Medicaid coverage, comorbidities, not filling high-intensity statin prescriptions before their myocardial infarction (ie, new users), and cardiac rehabilitation and outpatient cardiologist visits after discharge. Main Outcomes and Measures: High adherence to high-intensity statins at 6 months and 2 years after discharge was defined by a proportion of days covered of at least 80%, down-titration was defined by switching to a low/moderate-intensity statin with a proportion of days covered of at least 80%, and low adherence was defined by a proportion of days covered less than 80% for any statin intensity without discontinuation. Discontinuation was defined by not having a statin available to take in the last 60 days of each follow-up period. Results: Approximately half of the beneficiaries were women and fourth-fifths were white. At 6 months and 2 years after discharge among beneficiaries 66 to 75 years of age, 17 633 (58.9%) and 10 308 (41.6%) were taking high-intensity statins with high adherence, 2605 (8.7%) and 3315 (13.4%) down-titrated, 5182 (17.3%) and 4727 (19.1%) had low adherence, and 3705 (12.4%) and 4648 (18.8%) discontinued their statin, respectively. The proportion taking high-intensity statins with high adherence increased between 2007 and 2012. African American patients, Hispanic patients, and new high-intensity statin users were less likely to take high-intensity statins with high adherence, and those with dual Medicare/Medicaid coverage and more cardiologist visits after discharge and who participated in cardiac rehabilitation were more likely to take high-intensity statins with high adherence. Results were similar among beneficiaries older than 75 years of age. Conclusions and Relevance: Many patients filling high-intensity statins following a myocardial infarction do not continue taking this medication with high adherence for 2 years postdischarge. Interventions are needed to increase high-intensity statin use and adherence after myocardial infarction.