Intravenous digital subtraction angiography (IV DSA) has assumed a major role in the evaluation of occlusive cerebrovascular disease. However, an increasing incidence of inadequate and inaccurate IV DSA studies led us to use intra-arterial DSA (IA DSA) with greater frequency in the assessment of carotid artery disease. This study was performed to establish the optimal role of these two procedures in the diagnosis and management of carotid atherosclerosis. One hundred forty-eight patients who underwent carotid endarterectomy were assessed before operation with IV DSA (54 patients), IA DSA (41 patients), or conventional angiography (CA) (53 patients). Studies were reviewed for technical adequacy, extent of carotid visualization, contrast volume, incidence of complications, and necessity for further angiography. Subsequently the endarterectomy specimen was used to determine the accuracy of each imaging technique. The accuracy of IA DSA (94%) was significantly greater than that of IV DSA (68%) and no less than that of CA (97%) (p less than 0.0005). Only two IA DSA studies were technically inadequate (4%) compared with 26 of 65 (40%) IV DSA studies (p less than 0.0005). IA DSA consistently required less contrast agent (88 ml versus 144 ml) than did IV DSA (p less than 0.0005) but the extent of vessel visualization was greater. There was no difference in the complication rates of IV DSA and IA DSA, but both were less than that of CA (p less than 0.05). These data show IA DSA to be superior to IV DSA in the evaluation of carotid artery disease. IA DSA is now our preferred method of study and has increasingly supplanted CA techniques as well.