The carotid artery wall was studied with ultrasound in 23 children and adolescents with familial hypercholesterolaemia and in 23 age-matched healthy controls. The study revealed changes in the carotid artery wall related both to familial hypercholesterolaemia and to age. In the control subjects, the carotid artery wall became stiffer with age. In the patients with hypercholesterolaemia, no clear age-dependence was found, but wall stiffness correlated with total and low-density lipoprotein cholesterol. The intimal-medial wall thickness was associated with serum total cholesterol, low-density lipoprotein and triglyceride concentrations, and correlated inversely with the ratio of high-density lipoprotein to total cholesterol. Carotid artery wall properties seem to be associated with the degree of hypercholesterolaemia and the high-density lipoprotein-to-total cholesterol ratio even in children. In childhood and adolescence it is already possible, with ultrasound, to detect changes in the arterial wall related both to familial hypercholesterolaemia and to age.