We reviewed extracranial carotid studies in two groups of patients. The first group consisted of 200 patients who had been evaluated by both duplex scanning (DS) and direct arch-selective carotid arteriography (SCA). The second group consisted of 100 patients who had been evaluated by both intravenous digital subtraction angiography (IDSA) and conventional SCA. In 200 patients DS disclosed a 92% accuracy in delineating stenotic internal carotid disease and was accurate in recognizing ulcerative disease in 76% of patients. A review of the 100 patients studied by both IDSA and SCA showed that in 40% IDSA gave excellent correlation with SCA; in 35%, good correlation; and in 25%, poor correlation. In 10% DS was more accurate in delineating ulcerative disease than was IDSA, and on occasion DS was even more diagnostic than SCA. The relative accuracy, cost, risk, and clinical usefulness of each carotid diagnostic modality are discussed.