Niemann-Pick disease (type C) (NPC) is an autosomal recessive hereditary disease in which sphingomyelin and cholesterol are deposited in various organs of the body. The clinical manifestations of NPC include neurologic symptoms and cataplexy; other symptoms related to sleep have seldom been reported. One previous study described various sleep disorders including chronic insomnia, obstructive sleep apnea, restless leg syndrome, and rapid eye movement sleep behavior disorder, thus suggesting that sleep disorders in NPC patients are more prevalent than previously thought and warrant close attention. Here, we describe sleep disorders in two NPC patients and discuss the clinical characteristics and, for the first time, discuss potential pathogenic mechanisms underlying sleep disorders in such patients.© 2022 American Academy of Sleep Medicine.