Obstructive sleep apnea (OSA) is a common disorder and the major sleep-related risk factor for cerebrovascular disease. There is a dose-response relationship between the severity of OSA and the odds ratio for development of systemic hypertension. Observational studies have shown that patients with clinically significant OSA have increased incidence of cardiovascular and cerebrovascular disease, as well as increased incidence of sudden death in sleep. Following stroke, patients have a high prevalence of OSA, which diminishes the potential for rehabilitation, increases the risk of secondary stroke, and heightens mortality. Successful treatment of OSA with noninvasive positive airway pressure ventilation and with mandibular advancement devices lowers mean blood pressure. There is suggestive evidence that in patients with advanced OSA, permanent structural cerebral lesions may occur. Circadian changes during sleep contribute to an increase in the risk of cardiovascular and cerebrovascular accidents.