Apo C-II has a central role in triglyceride metabolism as a cofactor for lipoprotein lipase (LPL), the enzyme that catalyzes the hydrolysis of triglycerides on plasma lipoproteins. Apo C-II deficiency is a rare genetic disorder that is inherited as an autosomal recessive trait. Patients with this syndrome have marked alterations of triglyceride metabolism which include elevated fasting triglycerides, chylomicrons, and VLDL. Clinical features also include lipemia retinalis, eruptive xanthomas, and an increased incidence of pancreatitis. The initial description of the first patient with apo C-II deficiency by Breckenridge et al. established the important role of apo C-II as a cofactor for LPL. Since then, many kindreds with apo C-II deficiency have been described and the underlying molecular defect characterized.