Blood flow in the cervical carotid bifurcation was investigated by cine magnetic resonance imaging. In patients without stenosis, a low-intensity stream was demonstrated from the beginning of the carotid bulb, which was more distinct in the systolic phase. In patients with stenotic carotid bifurcations, the low-intensity flow was also present but was more prominent than in the non-stenotic bifurcation. This low-intensity stream may be due to the change from steady to turbulent flow due to the geometric characteristics of the carotid bifurcation or atheromatous plaque, similar to the flow separation phenomenon in fluid dynamics because of the coincidence of location and flow pattern. After carotid endarterectomy, turbulent flow was seen at the proximal and distal ends of the endarterectomy. Close follow-up and administration of antiplatelet agents are necessary to prevent restenosis due to mural thrombosis induced by such turbulent flow.