The study was motivated by the increasing recognition of the frequent occurrences of sleep-disordered breathing in the general population and mounting evidence that sleep-disordered breathing may increase risk for cardiovascular diseases, including coronary artery disease and stroke, and for hypertension, and may reduce quality of life generally. Many clinical questions remain unanswered concerning sleep-disordered breathing as well: for example, when, in the natural history of the disorder, intervention is warranted; and how to determine who is at risk so that recently developed treatments can be applied in a cost-effective manner.