The onset of coronary atherosclerotic plaques was investigated in 400 selected cases aged 1--40 years. During childhood the atherosclerotic plaques developed on their own, in preexisting branch pads or cushions. During adolescence the atherosclerotic plaques developed on their own, in both branch pads or cushions and thickened intimas. In young and mature adults the thickened intima became the main site for plaque histogenesis, whereas the role of branch pads or cushions decreased significantly. In mature adults incorporated microthrombi were accidentally involved in plaque development. In both branch pads or cushions and thickened intimas the atherosclerotic plaques developed through several stages including: histolysis, followed by nodular proliferation of smooth muscle cells (prevalent during childhood), insudation (prevalent during adolescence), accumulation of lipid-filled and foam cells (prevalent during early adulthood) and necrosis (prevalent in mature adults). Likewise the coronary fatty streaks developed on their own, through several stages, from early to advanced lesions. We were unable to reveal the conversion of fatty streaks into atherosclerotic plaques the two types of lesions occurring as unrelated pathological processes.