For several decades, clinical trials have addressed the question of whether treatment of hyperlipidemia reduces the risk of cardiovascular events. Substantial evidence supports the idea that cardiovascular benefits are related to the degree of reduction in low-density lipoprotein cholesterol level and perhaps to the degree of increase in the high-density lipoprotein cholesterol level. In these trials, changes in lipid levels have usually been small and the overall clinical benefits have been limited. The appearance in the 1980s of more effective treatments for hyperlipidemia, new arteriographic methods for assessing atherosclerosis, and new insights into atherogenesis permitted an objective investigation into whether the progression of atherosclerosis was retarded or reversed by lipid-lowering agents.