There is a renewed interest in the study of plaque lipid composition because it is recognized that it, rather than the luminal narrowing, influences the plaque stability and determines patient symptoms. At this purpose, we quantitatively evaluated in the carotid plaque of different categories of patients the expression of triglycerides, phospholipids, cholesterol, free cholesterol, esters of cholesterol, and the percentages of the three-phases (cholesterol, esters of cholesterol, phospholipids) by using the "Roozeboom triangle". Significant differences in the content of specific lipid and the percentage of the three-phases were detected among the different types of plaque evaluated in this study. The analysis of the three-phases by "Roozeboom triangle" may open a new approach in the study of atheromatous plaque and give new information on development of the disease.