Background: Statins are effective for the primary and secondary prevention of coronary heart disease (CHD) events. However, studies from the early 2000s have suggested that many patients have low adherence to statin therapy. Objective: To analyze trends in adherence among US adults initiating treatment with a statin. Methods: We identified US adults 21-64 years of age with commercial health insurance in Marketscan and ≥65 years of age with government health insurance through Medicare who initiated statin therapy in 2007-2014. Three populations were analyzed, those initiating statin therapy 1) following myocardial infarction (n=52,828 in Marketscan, n=148,745 in Medicare), 2) with diabetes without a history of CHD (n=565,573 in Marketscan, n=42,411 in Medicare), and 3) without diabetes or a history of CHD (n=2,134,501 in Marketscan, n=105,948 in Medicare). Adherence to statin therapy was defined by having a statin available to take for ≥80% of the 365 days following treatment initiation. Results: Adherence to statin therapy increased in each population analyzed ( Figure ). In 2014, 68.1% and 62.7% of patients initiating treatment following myocardial infarction in Marketscan and Medicare, respectively were adherent to their statin. Less than half of patients initiating treatment with diabetes without CHD and without diabetes or CHD in Marketscan and Medicare were adherent to their statin. Adherence to statin therapy in the overall Marketscan and Medicare populations was higher among men (relative risk [95% CI] 1.16 [1.15, 1.18] and 1.10 [1.08, 1.12], respectively), and those with cardiologist visits (1.22 [1.21, 1.24] and 1.27 [1.25, 1.30], respectively), and lower among those with kidney disease diagnosed after treatment initiation (0.89 [0.85, 0.94] and 0.92 [0.88, 0.96], respectively). Conclusion: Adherence to statins improved slightly between 2007 and 2014 but remains suboptimal. Management by a cardiologist is associated with better adherence to statins.