One hundred carotid bifurcations in young asymptomatic volunteers were examined with color Doppler flow imaging in an attempt to determine the frequency, configuration, magnitude, and duration of flow reversal. Areas of flow reversal were identified in all but one bifurcation. Just proximal to the bifurcation, flow reversal was typically located peripherally, opposite the origin of the external carotid artery. Distal to the bifurcation, flow reversal in the internal carotid artery typically assumed a linear configuration in the center of the vessel, extending from the superficial to the deep wall. Variations of these patterns were common. On the average, flow reversal occupied 33% of the lumen of the carotid bulb and extended for a distance of 14 mm. The average duration of flow reversal was 22% of the total cardiac cycle, with reversal typically occurring at peak systole and being replaced by static blood during diastole. These findings indicate that flow reversal in the carotid bifurcation is a normal phenomenon with a variable configuration, magnitude, and duration.