Plasma cholesteryl ester transfer protein facilitates the transfer of cholesteryl ester from HDL to apolipoprotein B-containing lipoproteins, and is a key protein in the reverse cholesterol transport system. The importance of plasma cholesteryl ester transfer protein in lipoprotein metabolism was highlighted by the discovery of deficient individuals with a marked hyper-HDL-cholesterolemia. Cholesteryl ester transfer protein deficiency causes various abnormalities in the concentration, composition, and functions of both HDL and LDL. Its significance in atherosclerosis is still controversial. However, in-vitro evidence shows large cholesteryl ester-rich HDL particles in cholesteryl ester transfer protein deficiency are defective in cholesterol efflux. Recent epidemiological studies have demonstrated an increased incidence of coronary atherosclerosis in deficient patients. The current review will also focus on the molecular genetics of the protein.