This chapter deals with established correlates of intima-media thickness (IMT) as well as new findings and formulations of data derived from this technology. The reliability and validity of the method are well described as are the relationships with risk factors, although new risk factors continue to be tested for associations with IMT. Differences in progression are now routinely used to define surrogate outcomes for clinical trials of behavioral and pharmacologic intervention; the Food and Drug Administration (FDA) accepts this as a valid marker of atherosclerosis change. Of considerable interest are insights that B-mode ultrasound provides into the process of vascular remodeling. The chapter discusses the associations of IMT with prevalent as well as incident coronary artery and cerebrovascular disease. Thus B-mode ultrasound has clearly become a mature technology for quantification and monitoring of the extent and progression of IMT of the extracranial carotid arteries.