Sleep-disordered breathing (SDB) refers to a spectrum of respiratory disturbances during sleep which ranges from snoring unaccompanied by functional disturbances to clinically overt obstructive sleep apnea syndrome. SDB has been implicated as a risk factor for the development of hypertension, ischemic heart disease, and cerebral infarction. It remains uncertain whether the risk of vascular disease associated with SDB exists independent of other known vascular disease risk factors, and if so, by what physiologic mechanisms. The association of SDB with increased sympathetic nervous system activity, which has potentially important adverse effects on blood pressure, left ventricular mass, lipid profile, platelet function, and atherogenesis, suggests a plausible mechanism for an independent adverse effect of SDB on the risk of cardiac, cardiovascular, and cerebrovascular disease (collectively, CVD). We propose to evaluate the independent contribution of SDB to the risk of CVD, and to study the mechanisms underlying this risk by means of a prospective longitudinal cohort study. This study will be conducted in the well-characterized Offspring Cohort, and a newly recruited Minority Cohort, of the Framingham Heart Study, as part of a larger collaborative study of the cardiovascular consequences of sleep apnea. We will address the following specific aims, (1.) Determine the risk of cardiovascular and cerebrovascular disease associated with SDB, independent of other known risk factors for CVD. (2.) Assess potential interactions between SDB and other known CVD risk factors in relation to CVD risk. (3.) Examine the contribution of SDB to the development of other CVD risk factors. (4.) Identify population subgroups at greatest risk of CVD from SDB. (5.) Estimate the effect of SDB on quality of life and utilization of health care resources. (6.) Test the hypothesis that isolated REM-associated SDB is a risk factor for CVD. (7.) Test the hypothesis that SDB increases the risk of CVD by increasing the activity of the sympathetic nervous system. (8.) Test the hypothesis that level of ventilatory function, as measured by spirometry, modifies the risk of CVD associated with SDB.