Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral lipid storage disorder, but the basic defect has not yet been clarified. Diagnostic biochemical makers are intracellular accumulation of free cholesterol or the decreased esterification of exogenous cholesterol. The differences in the severity of defective esterification are related to the onset of the disease. Genetically, an abnormal gene is located on the human chromosome 18. Biochemically, many drugs, i.e. imipraine, progesterone and bafilomycin A1 are known to interfere with cholesterol esterification. Clinically, vertical supranuclear gaze palsy and cataplexy are specific symptoms. The filipin stain of the foamy cell in bone marrow is available for rapid diagnosis. Many therapies, i.e. dimethyl sulfoxide, low-cholesterol diet and transplantations, have been challenged but improvement of neurological symptoms have not been reported.