['Cerebral infarction of unknown origin at admission accounts for half of all cerebral infarction cases in some institutions. However, the factors associated with cerebral infarction prognosis have not been sufficiently examined. Here, we investigated whether aortic arch plaques (AAPs) on transoesophageal echocardiography (TOE) were associated with the prognosis of cerebral infarction of unknown origin at admission.', 'Of 571 patients who were hospitalised between June 2009 and September 2011, 149 (age: 67 ± 14 years; 95 men) with cerebral infarctions of unknown origin at admission underwent TOE and were enrolled in this study. We examined their clinical characteristics, the incidence of intermittent atrial fibrillation detected on 24-hour electrocardiography, and the echographic findings of the carotid artery in the hospital. A poor prognostic outcome was defined as a modified Rankin Scale score of ≥3 after 90 days.', 'In all, 110 patients (74%) showed good prognoses and 39 patients (26%) showed poor outcomes. A National Institutes of Health Stroke Scale score of >6 on admission [odds ratio (OR) = 6.77; 95% confidence interval (CI): 2.59-18.8; p < 0.001] and AAPs of ≥4 mm (OR = 2.75; 95% CI: 1.19-6.91; p = 0.024) showed significant associations with a poor prognosis of cerebral infarction of unknown origin at admission.'] Does aortic arch atherosclerosis in ischaemic stroke of unknown origin affect prognosis?