A major emphasis of the study is its focus on subclinical disease, or abnormalities detected noninvasively without signs or symptoms. Subclinical disease measures in CHS include ultrasonography of the carotid artery and abdominal aorta, ankle-brachial index, echocardiography, resting and ambulatory electrocardiography, cerebral magnetic resonance imaging, spirometry, and retinal photography. Some of these measures are conducted three times; at baseline, to assess risk of clinical disease in relationship to subclinical disease; three to four years after entry to assess change in subclinical disease and risk of clinical disease in relationship to change; and toward the end of the study, to assess predictors of subclinical disease itself. Echocardiography, ambulatory ECG, cerebral MRI and aortic ultrasonography will only be conducted twice.