The doctrine of self-fulfilling prophecy has been invoked in studies of the effects of sex chromosome aneuploidy on human development as a reason for routine concealment of the diagnosis from affected children and their families. It has been assumed that knowledge of the existence of risk for deviance from normal development automatically creates a self-defeating emotional climate. This communication attempts to delineate both advantageous and deleterious aspects of self-fulfilling prophecy in the medical management of sex chromosome aneuploidy, present at alternative approach, and reviews the experience in a prospective study of 52 families where a policy of disclosure was followed.