Blunt traumatic occlusion or stenosis of the internal carotid artery is a rare complication of whiplash injury and may not be recognized until the onset of neurological symptoms. The clinical course can vary considerably, with regard to both the symptoms and the interval between injury and manifestation. A dissecting aneurysm and intimal tear are usually observed after blunt internal carotid artery injury. Atherosclerotic plaque is often observed in the cervical internal carotid artery and carotid bifurcation, but involvement of plaque has been confirmed in relatively few cases of blunt traumatic internal carotid injury. We describe a 58-year-old man who developed cerebral embolism due to intraplaque thrombus after a minor whiplash injury and was successfully treated with carotid endarterectomy. Because thrombosis occurred within the atherosclerotic plaque, we named the mechanism of this case "plaque injury".