A survey of 40 individuals registered with the Canadian National Institute for the Blind (CNIB) as blind from congenital nystagmus revealed that an abnormal single gene was responsible for the disorder in 33 patients. Fifteen of these were due to autosomal recessive conditions while X-linked disorders accounted for another 15 patients. In 3 cases the pedigrees were consistent with both autosomal recessive or X-linked inheritance. A clearly defined environmental origin was present in 1 case while specific genetic or environmental factors were not detected in the remaining six patients. The albinism, achromatopsia and Leber's congenital amaurosis groups of disorders were those most frequently detected.