Obstructive sleep apnea (OSA) is a common sleep disorder, and research on the effects of sleep apnea is important to gain insight into how sleep affects health. Untreated OSA has been associated with important health consequences, such as an increased risk for hypertension, cardiovascular disease and diabetes. Previous studies have shown that OSA also represents a risk factor for stroke. The relationship between OSA and stroke is particularly relevant, as stroke is the second leading cause of death globally. The reviewed article presents new data from the Sleep Heart Health Study, a longitudinal cohort study, which shows an association between incident stroke and untreated OSA of varying severity for men and possibly more severe OSA for women. The study is discussed in the context of the current state of knowledge about OSA, in particular its health consequences, and the general limitations in conducting research with OSA patients.