Duplex ultrasound has supplanted almost every other noninvasive diagnostic test to evaluate patients with suspected cerebrovascular disease. Improvements in technology and expertise in interpretation have led to reliance on duplex testing in many cases as the sole diagnostic test in these patients with few limitations. While plaque characterization is important, physiologic hemodynamic measurements are very accurate in determining the degree of stenosis in carotid, vertebral, and intracranial arterial systems. Multispecialty consensus criteria have now been established for vascular laboratories that do not have internally validated criteria of their own. Accreditation of vascular laboratories has resulted in an expectation of minimal baseline quality of testing. Advances continue to occur in further refinement of equipment, new imaging tools, and interpretation criteria.