AIMS: Sacubitril/valsartan is strongly supported in guidelines for the management of heart failure, but suboptimal adherence and treatment non-persistence may limit the population-level benefit that this therapy might otherwise offer. METHODS AND RESULTS: We identified a cohort of Medicare beneficiaries (2014-2017) initiating sacubitril/valsartan after >/=6 months of continuous enrolment. We assessed adherence as the proportion of days covered (PDC) and proportion of patients non-persistent (having no prescription available) at 180 days after initiation. We fit a multivariable negative binomial model with a count of adherent days to evaluate independent factors associated with of sacubitril/valsartan adherence. Among 27 063 new sacubitril/valsartan users, most (n = 17 663, 65%) were prescribed low-dose at 24 mg/26 mg and most (n = 19 984, 74%) were switched from prior angiotensin-converting enzyme inhibitor/angiotensin receptor blocker (ACEi/ARB) rather than being RASi treatment naive. Median 180-day PDC was 86% (25th-75th percentiles 58-98%). Black patients, those with high comorbid disease burden (>/=8 comorbidities), and patients with recent hospitalization within 30 days had fewer adherent days, while those treated with preceding ACEi/ARB had more adherent days. Thirty-four percent of patients did not have an active sacubitril/valsartan prescription at day 180. Among these, few had preceding dose down-titrations (6% among patients on 49 mg/51 mg and 9% among patients on 97 mg/103 mg) and 68% did not have a subsequent ACEi/ARB prescription. Among patients who remained persistent, dose up-titrations occurred in 29% of patients who started on 24 mg/26 mg and 27% of patients on 49 mg/51 mg. CONCLUSIONS: Overall adherence to sacubitril/valsartan among Medicare beneficiaries is acceptable, but is lower in Black patients, those with higher comorbidities or those who started therapy after recent hospitalization. While broad implementation of guideline-directed medical therapy is a key priority, additional focused efforts to improve adherence early after hospitalization and among at-risk patients are needed in parallel.