['Sleep-disordered breathing (SDB) is a risk factor for cerebrovascular disease. We investigated the frequency of SDB in Japanese patients with acute ischaemic stroke and transient ischaemic attack (TIA), as well as factors associated with SDB severity.', 'Between April 2010 and March 2011, we prospectively enrolled patients with ischaemic stroke and TIA within 24 h of onset to participate in a sleep study within 7 days of admission. We defined SDB as a respiratory disturbance index (RDI) (number of apnoeas or hypopnoeas per hour) of ≥ 5. Patients were assigned to groups based on RDI values of ≥ 30 (severe) and <30 (absent or not severe). The frequency of SDB and factors associated with severity were investigated using multivariate regression analysis.', 'We enrolled 150 patients amongst whom 126 (84%) had SDB. The frequencies of SDB were 21 (75%) patients with TIA, 105 (86%) with ischaemic stroke, 8/10 (80%) with large artery atherosclerosis, 14/14 (100%) with small vessel occlusion, 37/41 (90%) with cardioembolism and 46/57 (81%) with other causes of stroke/undetermined. Severe SDB was evident in 44 (29%) patients. The frequency of males (75% vs. 56%, P = 0.027), atrial fibrillation (AF) (39% vs. 23%, P = 0.045), higher body mass index (23.8 ± 3.8 vs. 22.3 ± 3.8, P = 0.043) and a larger neck circumference (37.8 ± 4.3 vs. 35.8 ± 4.2, P = 0.012) was significantly higher in the group with severe SDB. Multivariate regression analysis found that AF (OR 2.4; 95% CI 1.079-5.836, P = 0.0359) was independently associated with severe SDB.'] Is atrial fibrillation associated with severe sleep-disordered breathing in patients with ischaemic stroke and transient ischaemic attack?