Patients with heterozygous and homozygous Familial Hypercholesterolemia exhibit a high incidence of premature coronary heart disease, presumably due to atheromatous plaque-formation in the coronary arteries. Clinical symptoms develop when the disease has progressed to more severe stages of atherosclerosis. Aim of our study was to visualize and document early atheromatous lesions in the carotid arteries of asymptomatic patients with familial hypercholesterolemia under 30 years of age by Duplex-scan. Of 44 patients, 70% had detectable carotid plaques, while only 12% of the controls were affected. All patients with severe carotid disease had serum cholesterol levels above 350 mg/dl. In the age group 2-20 years, 66% of the patients exhibited plaques. Only 6% of the FH patients 21-30 years had normal carotid arteries. We conclude that the process of atheromatous plaque formation in patients with FH starts early in life, severity of atherosclerosis being a function of both extent and duration of hypercholesterolemia. Duplex-scan examination of the carotid arteries is efficient and precise non-invasive method suitable to visualize this process and, by measuring regression, monitor the efficacy of therapeutic measures.