Obstructive sleep apnea (OSA) and stroke are frequent, multifactorial entities that share risk factors, and for which case-control and cross-sectional studies have shown a strong association. Stroke of respiratory centers can lead to apnea. Snoring preceding stroke, documentation of apneas immediately prior to transient ischemic attacks, the results of autonomic studies, and the circadian pattern of stroke, suggest that untreated OSA can contribute to stroke. Although cohort studies indicate that OSA is a stroke risk factor, controversy surrounds the cost-effectiveness of the screening for and treatment of OSA once stroke has occurred.