Background: Non-stenotic intracranial and systemic atherosclerosis are associated with ischemic stroke. We report frequency and response to anticoagulant vs. anti-platelet prophylaxis of patients with embolic stroke of undetermined source (ESUS) who have non-stenotic intracranial atherosclerosis and/or systemic atherosclerosis. Methods: Exploratory analysis of the international NAVIGATE ESUS randomized trial comparing rivaroxaban 15mg daily with aspirin 100mg daily in 7213 patients with recent ESUS. Among participants with results of intracranial arterial imaging with either computed tomographic angiography (CTA) or magnetic resonance angi-ography (MRA), the frequency and predictors of non-stenotic intracranial and sys-temic atherosclerosis and responses to antithrombotic therapy were assessed. Results: Among 4723 participants with available intracranial CTA or MRA results (65% of the trial cohort), the prevalence of intracranial atherosclerosis was 16% (n=739). Patient features independently associated with intracranial atherosclerosis included East Asian region (odds ratio 2.7, 95%CI 2.2,3.3) and cervical carotid pla-que (odds ratio 2.3, 95%CI 1.9,2.7), among others. The rate of recurrent ischemic stroke averaged 4.8%/year among those with intracranial atherosclerosis vs. 5.0.%/year for those without (HR 0.95, 95%CI 0.65, 1.4). Among those with intracra-nial atherosclerosis, the recurrent ischemic stroke rate was higher if assigned to rivaroxaban (5.8%/year) vs. aspirin (3.7%/year), but the difference was not statistically significant (HR 1.6, 95%CI 0.78, 3.3). There was trend for the effect of antithrombotic treatments to be different according to the presence or absence of intracranial atherosclerosis (pinteraction=0.09). Among participants with evidence of systemic atherosclerosis by either history or imaging (n=3820), recurrent ischemic stroke rates were similar among those assigned to rivaroxaban (5.5%/year) vs. aspi-rin (4.9%/year)(HR 1.1, 95%CI 0.84, 1.5). Conclusions: East Asia region was the strongest factor associated with intracranial atherosclerosis. There were no statisti-cally significant differences between rivaroxaban and aspirin prophylaxis for recur-rent ischemic stroke in patients with non-stenotic intracranial atherosclerosis and/ or systemic atherosclerosis.