We examined coronary arteries of 200 autopsied cases of the youth (1 month to 39 years of age) in Kyushu island. The coronary arteries were stained by Sudan III and examined using by a point-counting method. Selected 52 cases were also histologically examined, the coronary arteries of which were taken from Seg. 1, Seg. 6, and macroscopically the most stenotic region. Atherosclerotic lesions were histologically classified four types: concentric fibrous, eccentric fibrous, concentric lipid-rich, and eccentric lipid-rich type. The degrees of stenosis were morphemetrically evaluated. The surface involvement and the atherosclerotic index were increased with age, and the latter was accelerated in the 4th decades. The majority of coronary atherosclerotic lesions with less than 50% stenosis were of concentric fibrous type. Lipid-rich type of lesions were increased in the coronary arteries with over 50% stenosis. Serum cholesterol levels of patients with a lipid-rich type of lesions were significantly higher than those with a fibrous type. These results suggest that the early stage of coronary atherosclerosis in the Japanese youth is mainly of a concentric fibrous type and it develops to an eccentric fibrous or lipid-rich type. Hypercholesterolemia would promote the progression of atherosclerosis.