Background <p>Obstructive sleep apnoea (OSA) is a common sleep-related breathing disorder that can negatively affect the prognosis of cardiovascular events. However, OSA may facilitate the development of collateral circulation via hypoxic preconditioning. This study aimed to investigate the relationship between OSA and intracranial collateral circulation among stroke patients with proximal middle cerebral artery (MCA) stenosis or occlusion.</p> Methods <p>Patients with symptomatic unilateral proximal MCA stenosis or occlusion were enrolled. All patients underwent polygraph and computed tomographic angiography within 72&#xa0;h of stroke onset. OSA was defined as an apnoea-hypopnoea index (AHI) of ≥ 15 events per hour. The collateral circulation of the MCA was visually assessed via the Tan scoring system and ranged from 0 (no collaterals) to 3 (extensive collaterals).</p> Results <p>Among the 78 enrolled patients, 74% were male. The mean age of the participants was 61 ± 12 years. OSA was identified in 40 patients (51.3%). Compared with non-OSA patients, OSA patients presented better intracranial collateral circulation (collateral score ≥ 2, 87.5% vs. 65.8%, <i>P</i> = 0.023). Additionally, patients with good intracranial collateral circulation (collateral score ≥ 2) had a greater AHI than patients with poor intracranial collateral circulation (25.4 ± 17.1 vs. 14.9 ± 13.2, <i>P</i> = 0.02). Spearman’s correlation analysis revealed a positive correlation between the AHI and collateral score (<i>r</i> = 0.866, <i>P</i> &lt; 0.01).</p> Conclusion <p>OSA may facilitate the development of intracranial collateral circulation in patients with proximal MCA stenosis or occlusion and thus exert protective effects among patients with acute cerebral infarction.</p>