NIEMANN-Pick disease is an inborn error of lipid metabolism characterized by abnormal accumulation of sphingomyelin in various organs. Crocker1divided the disease into the following four subgroups based on the combined clinical and chemical studies: classical infantile form (type A), visceral form (type B), subacute or juvenile form (type C), and Nova Scotian variant (type D). This classification seems to be generally accepted, but the well documented adult Neimann-Pick disease2,3can be added as the fifth form. A recent investigation4indicated that the deficiency of sphingomyelinase, an enzyme which hydrolyzes sphingomyelin, is the basic enzymatic defect of Niemann-Pick disease. A more comprehensive study5of this enzyme revealed its deficiency only in the infantile and visceral forms. According to Crocker,1the classical infantile form is the only one showing increased sphingomyelin in the brain. A characteristic pathological change of the central nervous system in infantile Niemann-Pick