Sleep apnea is defined as present if the AHI is 5 events per hour, and an increasing AHI indicates Several longitudinal studies have identified sleep apnea as an independent risk factor for stroke. The first prospective data demonstrating an association between sleep apnea and stroke risk came from the Wisconsin Sleep Cohort Study.732 This cohort included 1189 subjects followed up for 4 years. There was a 3-fold increase in the risk of stroke (OR, 3.09; 95% CI, 0.74 12.81) for subjects with an AHI 20 events per hour. The Sleep Heart Health Study followed up 5422 adults who were 40 years of age without a history of stroke but with untreated sleep apnea for a median of 8.7 years.733 The unadjusted stroke risk associated with sleep apnea was somewhat higher in men than in women; the OR for ischemic stroke per 10 years was 2.26 (95% CI, 1.45 3.52) for men and 1.65 (95% CI, 1.45 3.52) for women. After adjustment for age, BMI, race, smoking, SBP, antihypertensive medica- tions, and diabetes mellitus, sleep apnea was associated with stroke risk in men but not women. Among men, there was a progressive increase in ischemic stroke risk with increasing sleep apnea severity: AHI 9.5 to 19.1 events per hour, adjusted OR, 1.86 (95% CI, 0.70 4.95); AHI >19.1 events per hour, adjusted OR, 2.86 (95% CI, 1.10 7.39). A meta-analysis of 5 prospective studies that included 8435 participants identified an OR for incident stroke risk of 2.24 (95% CI, 1.57 3.19).734 This meta-analysis also found that increased stroke risk is associated with increasing sleep apnea severity with an OR of 1.35 (95% CI, 1.25 1.45) for every 10-unit increase in AHI. 