A new neurological rat mutation showing hind-leg paralysis, cerebellar vermis defect, and cerebellar cortical dysplasia was named "cerebellar vermis defect" (CVD). Pathologically, affected animals already had a small-sized cerebellum in newborns and started to show hind-leg paralysis at approximately 14 days of age. The CVD rat was fertile in both sexes. Genetic analysis indicated that the CVD character is controlled by an autosomal recessive gene with 100% penetrance. The proposed gene symbol is Cvd.