Fibromuscular intimal thickening begins to occur early in the pediatric age, with or without lipid deposition. Fatty streaks also appear first in infant. Fatty streaks occur almost always in close association with intimal thickening. Some fatty streaks remain unchanged as those seen in the ascending aorta. Intimal thickening and lipid deposition generally increase with age. The prevalence of those lesions is very high in infants and children. The degree and extent of those lesions display wide individual variability. Finally, intimal thickening is considered to be an integral part of atherosclerosis and to represent the first stage of atherosclerosis. Atherosclerotic lesions, at least a part of them, are derived from thrombosis in association with endothelial denudation. Hyperlipidemia accelerates the atherosclerotic process. Lipid-rich atherosclerotic lesions may regress to some degree under a long normolipidemic state but leave intimal fibrous scarring. Therefore primary prevention of atherosclerosis should be directed as well as secondary prevention.