A family having one member with Norrie's disease, X-linked retinal dysplasia associated with hearing loss and mental retardation, was studied using DNA markers. The DNA markers were used to try and confirm the diagnosis of Norrie's disease by detecting a deletion of the X chromosome. Linkage analysis using the polymorphic DNA markers was performed and this allowed more accurate determination of the carrier status of two sisters of the affected boy than by empiric risk calculation. The advantage of multiple polymorphic DNA markers for linkage analysis is illustrated.