The association of disturbances of plasma lipid transport and atherogenesis has been recognized, and scientific data continue to accumulate to explain this association from a mechanistic viewpoint. A number of recent clinical trials have shown that cholesterol-lowering therapy can prevent the complications of atherosclerosis. Consequently, the attention of physicians to therapeutic intervention has increased and public awareness to plasma cholesterol levels has been heightened. This article summarizes current knowledge of how plasma lipid transport is regulated. The classical primary hyperlipoproteinemias are considered and hyperlipoproteinemias occurring secondary to other diseases are discussed. Standard methods to diagnose the defined genetic hyperlipidemias are outlined, and new approaches to assess risk of atherosclerosis are examined. Finally, the role of dietary measures and drugs in lowering blood lipids and reducing risk of coronary heart disease is delineated.