The carotid bifurcation plaque is a common pathology. Specific pathologic atheromatous findings have been studied in three hundred patients-carotid bifurcations. This study was carried with the Doppler technics and especially the spectral analysis of the Doppler. From that study it appeared that the most frequent disturbances could be classified according five grades, corresponding to the importance of the stenosis. The first grade corresponds to a stenosis responsible of an obstruction less than 40% of the vessel. The second one is a stenosis from 40% to 60% of the lumen. The third grade is the witness of a extended plaque and a stenosis between 60% to 75%. The fourth grade corresponds to a stenosis between 60% and 90%. The fifth grade is a stenosis superior to 90% of the surface of the artery, also called pre-occlusive grade. This ultrasonic method has been compared to the data provided by the angiography, the echotomography and the anatomopathology. The correlation is excellent in the three cases, and is of 95%. The authors emphasize that this method is the most accurate among the non invasive investigations and let hope that it might replace the traumatic ones in the future.