We report a Caucasian family in which four males out of a total of seven siblings are mentally retarded. Three of the affected individuals have spasticity in the lower limbs (spastic paraplegia), pes cavus deformity of both feet and an abnormal gait. In addition, they show palmar and plantar hyperkeratosis. The other male sibling does not have spasticity, but his lower limb reflexes are abnormally brisk and he has slight pes cavus deformity. He also shows hyperkeratosis of his palms and soles and is less mentally retarded that his brothers. The mother of the affected boys has normal intelligence, but has plantar hyperkeratosis and a strong facial resemblance to her retarded sons. Her three daughters are normal. The pedigree information is compatible with a sex-linked mode of inheritance and no specific biochemical or cytogenetic abnormality has been found in the affected individuals. There have been no previous reports of hyperkeratosis palmaris et plantaris in other inherited spastic syndromes.