The relationships between obstructive sleep apnoea syndrome (OSAS) and stroke are still under discussion, but increasing evidence demonstrates that the OSAS is an independent risk factor for stroke. However, in rare cases, OSAS could be a consequence of strokes, especially if located in the brainstem. Many recent studies have found a 70 to 95% frequency of OSAS (defined by an apnoea/hypopnoea index >10) in patients with acute stroke. Age, body mass index, diabetes, and severity of stroke have been identified as independent predictors of stroke. Furthermore, the presence of OSAS in stroke patients could lead to a poor outcome. The potential mechanisms linking OSAS and stroke are probably multiple (arterial hypertension, cardiac arrhythmia, increased atherogenesis, coagulation disorders, and cerebral haemodynamic changes). Despite numerous uncertainties, OSAS should be systematically screened at the moment it is clinically suspected in patients with acute stroke. However, the optimal timing (early or differed) for treatment with nasal continuous positive airway pressure remains to be determined.