The dyslipidemia typically found in subjects with the metabolic syndrome includes an elevated concentration of plasma triglyceride,a low-density lipoprotein fraction in which the particles are smaller and denser than normal, and a low concentration of highdensity lipoprotein (HDL) cholesterol. This article is concerned with the low HDL component. It provides an overview of HDL structure and metabolism and describes the functions of HDLs that may be cardioprotective. The article then outlines what is known about the concentration and subpopulation distribution of HDLs in the metabolic syndrome. Possible mechanisms responsible for the low HDL are discussed. The consequences of a low HDL concentration in this syndrome are addressed before the article concludes with a discussion of whether low HDL in the metabolic syndrome should be a therapeutic target.