Four pedigrees, each with two or more cases of congenital superior oblique palsy among immediate family members, are presented. Except for a single case report in 1926, this disorder has not been known to occur in a hereditary manner. Theories of pathogenesis of congenital fourth cranial nerve palsy are discussed, with special reference to the hereditary occurrence of this disorder. Analogy is drawn between the familial forms of congenital superior oblique palsy and Duane's syndrome.