We evaluated the serum levels of lipoproteins and apolipoproteins in patients with angiographically proven extracranial and/or intracranial carotid atherosclerosis (ECA and/or ICA). The prevalence of hypertension, diabetes mellitus and smoking was significantly higher in patients with carotid atherosclerosis. Total HDL-cholesterol, HDL2-cholesterol and HDL3-cholesterol were higher in patients with carotid atherosclerosis than in patients without carotid atherosclerosis. The serum concentration of apolipoprotein A-I and A-II were significantly low in patients with ICA alone, ECA + ICA, bilateral carotid stenosis, and unilateral carotid occlusion. These data suggested that decreased serum HDL cholesterol and apolipoprotein A-I are potential indicators of the progression of carotid atherosclerosis in association with hypertension, diabetes mellitus and cigarette smoking.