Cystic fibrosis (CF), which is caused exclusively by mutation of a single gene, is inherited in autosomal recessive fashion and is the commonest such disorder in populations of Caucasian origin. Although much progress has been made during the last 50 years in its clinical management, with a corresponding improvement in the mean life expectancy in developed countries from a few months to a few decades, it remains incurable and a complete understanding of its biochemical basis is still being sought. Consequently, attention has been given to the possibility of screening for carriers of the defective gene, who represent up to 5% in some populations, so that they may be given appropriate genetic counselling. Whereas previously carriers were identified only when they became parents of affected children, in recent years carriers who were more distantly related to CF patients have often been identified by means of genetic linkage techniques. A new strategy for the control of CF at the population level is now proposed. It is based on the report of a joint WHO/ICF(M)A (International Cystic Fibrosis (Mucoviscidosis) Association) Task Force on CF which met in November 1990.