Background Sleep‐disordered breathing ( SDB ) after acute ischemic stroke is frequent and may be linked to stroke‐induced autonomic imbalance. In the present study, the interaction between SDB and peripheral endothelial dysfunction ( ED ) was investigated in patients with acute ischemic stroke and at 1‐year follow‐up. Methods and Results SDB was assessed by transthoracic impedance records in 101 patients with acute ischemic stroke (mean age, 69 years; 61% men; median National Institutes of Health Stroke Scale, 4) while being on the stroke unit. SDB was defined by apnea‐hypopnea index ≥5 episodes per hour. Peripheral endothelial function was assessed using peripheral arterial tonometry (Endo PAT ‐2000). ED was defined by reactive hyperemia index ≤1.8. Forty‐one stroke patients underwent 1‐year follow‐up (390±24 days) after stroke. SDB was observed in 57% patients with acute ischemic stroke. Compared with patients without SDB , ED was more prevalent in patients with SDB (32% versus 64%; P <0.01). After adjustment for multiple confounders, presence of SDB remained independently associated with ED (odds ratio, 3.1; [95% confidence interval, 1.2–7.9]; P <0.05). After 1 year, the prevalence of SDB decreased from 59% to 15% ( P <0.001). Interestingly, peripheral endothelial function improved in stroke patients with normalized SDB , compared with patients with persisting SDB ( P <0.05). Conclusions SDB was present in more than half of all patients with acute ischemic stroke and was independently associated with peripheral ED . Normalized ED in patients with normalized breathing pattern 1 year after stroke suggests a mechanistic link between SDB and ED . Clinical Trial Registration URL : https://drks-neu.uniklinik-freiburg.de . Unique identifier: DRKS 00000514.