Lysosomal acid lipase (LAL) is a lysosomal enzyme that is involved in intracellular lipid metabolism. Complete deficiency of the LAL enzyme causes Wolman disease, while reduced but residual LAL activity (approximately 2%-8% of controls in blood leukocytes) causes cholesteryl ester storage disease (CESD). Wolman disease is fatal within the first year of life due to severe hepatomegaly, persistent diarrhea and failure to thrive. CESD is a milder disease that is characterized by hyperlipidemia and hepatomegaly that can be observed in childhood or develop in adulthood. Several CESD patients with no typical clinical symptoms or with only mild liver enlargement even at an advanced age have also been reported. In general, CESD is not associated with a reduced life span although atherosclerosis and chronic liver disease have been identified as a premature cause of death. The incidence of CESD in the general population is not known but has been estimated at approximately 2.5 per 100,000, while Woman disease is extremely rare.