Abstract To evaluate ultrasonographically determined intima-media thickness as a measure of early atherosclerosis, three studies were performed. Ultrasound measurements of intimamedia thickness in the carotid artery were directly validated by comparing the same thickness measured by light microscopy. The values were closely correlated (r=.82, p<.001). Intima-media thickness determined by light microscopy was consistently smaller than that determined by ultrasound, probably due to shrinkage during histological preparation. As an indirect validation, mean intima-media thickness was calculated in three large groups of patients with no plaque (n=224), one plaque (n= 105), and one circumferential or two or more plaques (n=54) in the carotid bifurcation. Intima-media thickness increased significantly with increasing plaque score, indicating that diffuse intimamedia thickening is more pronounced with more severe atherosclerosis. The intima-media thickness also increased with increasing multifactorial cardiovascular risk, reflecting a positive relation between signs of early atherosclerosis and the burden of known risk factors for the disease.