Three hundred carotid plaques (stenosis 45 to 65%) in 300 asymptomatic patients were included into a follow-up study considering three ultrasound types of plaques: type 1, non echogenic; type 2 intermediate, partially echogenic and type 3 highly echogenic. Types 1 and 2 had regular contour/surface while type 3 was irregular and in some patients associated with ultrasonographic signs of ulceration and intra-plaque haemorrhage. Patients were clinically evaluated for 3 years, randomly selected subgroups were studied with cerebral CT or magnetic resonance (MR) scanning to evaluate brain damage. There were no signs of cerebral damage in type 1 plaque patients. The incidence of signs and symptoms were higher in type 2 and 3 plaque patients. This was associated with an increased incidence of CT lesions and an even higher incidence of MR lesions in plaque type 3. In conclusion type 3 plaques are associated both with more clinical problems and evidence of CT/MR brain damage. Furthermore MR reveals more brain lesions than CT.