Atherosclerotic lesions are responsible for about 10% of ischemic stro
kes. However, the evolving thrombotic and embolic potential of these l
esions remains difficult to evaluate. Pathology studies and ultrasonog
raphy have contributed to the study of the complications of atheroscle
rotic plaques at the origin of the internal carotid artery (hemorrhage
, ulceration, necrosis, and the degree of stenosis). Moreover, improve
ment of ultrasound examination of intracranial arteries allows the det
ection of emboli which could be markers of ulceration. Considering pat
hologic, angiographic, ultrasonographic and clinical studies, only tig
ht stenoses have been shown to have a high thromboembolic potential. T
he risk is further increased when the stenosis is ulcerated, progressi
ve, has an intraluminal thrombus, or when it is the source of emboli d
etected by transcranial Doppler. Apart from this stroke risk, an incre
ased general risk of vascular mortality and heart morbidity is present
in this population. Increased intima plus media thickness of the comm
on carotid artery, quantified by B-mode sonography, has been shown to
be a good predictor of ischemic events. Further improvements in noninv
asive methods will more precisely define the evolution of atherosclero
tic plaques and their link with the risk of stroke, especially for low
-degree stenosis.