Carotid stenosis is a common cause of ischemic stroke. The management of patients with a carotid lesion is mainly based on the degree of stenosis. Ultrasonography is a reliable and accurate method of quantification of the stenosis. The sonographic quantification is based on both velocity and morphological criteria. B mode, color or power Doppler as well as spectral Doppler are used for this purpose. The actual velocity criteria for a 70% stenosis (NASCET definition) are as follows: maximal systolic velocity above 230 cm.s-1, telediastolic velocity above 100 cm.s-1, carotid ratio above 4. The morphological quantification of the stenosis relies on Doppler imaging and B-mode coupling. With ultrasound, the residual area can be measured using a short axis plane, and the diameter reduction using a longitudinal plane. The different parameters provide complementary information that must be in agreement with one another. There is a growing interest in plaque characterization. Undoubtedly plaque structure and surface appearance also play a role in the individual risk of stroke. Thus, B-mode plaque analysis must be an integral part of the ultrasonographic examination. Transcranial Doppler is a complementary investigation that can be used to evaluate the hemodynamic consequences of the stenosis and to look for intracranial lesions. Optimal sonographic examination currently allows comprehensive evaluation of a carotid lesion.