Lipoprotein lipase (LPL) plays a major role in the regulation of lipid lipid metabolism. Its primary function is the hydrolysis of triglyceride core of chylomicrons and very low density lipoproteins. In addition, LPL activity allows the maturation of several classes of lipoproteins. Impaired lipolisys due to LPL deficiency causes hypertriglyceridemia and chylomicronemia syndrome. Two primary defects of LPL activity are known, the familial deficiencies of LPL and of apo CII, the natural cofactor of LPL. Circulating inhibitor of LPL has also been reported. Two paradigmatic cases of chylomicronemia syndrome due to familial LPL deficiency are described.