Hyperlipidemias represent a group of metabolic disorders characterized by an increase in plasma cholesterol or triglycerides, or both. Cutaneous or tendon xanthomas may or may not be present, depending on the severity of the lipid abnormality. A high incidence of coronary heart disease is a prominent feature in some forms of familial hyperlipidemias. Besides plasma lipid levels, the determination of plasma lipoprotein patterns adds a new criterion to the identification of this group of heterogeneous disorders. On the basis of abnormal lipoprotein patterns, five types of familial hyperlipidemias have been recognized. The interpretation of abnormal lipoprotein patterns is not only of diagnostic importance but also may reveal useful information as to the possible mechanism of a lipid metabolic derangement. Furthermore, a correct diagnosis is of the utmost importance to arrive at the proper treatment.