The folial pattern of the mouse cerebellum was compared in 13 inbred strains and a closed colony. The morphological variation of the cerebellum among individual animals was slight within each inbred strain, whereas it was marked in the closed colony. There was no sex-related difference in the cerebellar folial pattern. The cerebellum of mice from each inbred strain presented a characteristic folial pattern in which some similarities were recognized among animals from genetically related strains. These findings revealed that the morphological variation in the folial pattern of the cerebellum was strain-specific in mice and had an intimate connection with the genetic control.