Little has been published on cystic fibrosis (CF) in Whites in southern Africa, and no figures as to incidence exist. A register of CF patients, their parents (obligatory carriers), siblings, uncles, aunts and first cousins (potential carriers) has been compiled for southern Africa. The degree of co-operation shown by colleagues and by families whose addresses have been provided by them, and possible reasons for non-co-operation are discussed. From the numbers and birth dates of patients a rough estimate of the incidence in the Republic of South Africa, South West Africa and Rhodesia has been made. In all three regions, but especially in South Africa, incidence is likely to have been underestimated. Details available from the register include the number of CF patients alive and dead, those who presented with meconium ileus, the number of affected patients per family, consanguinity among the parents or grandparents, the frequency with which identical surnames were encountered, and the sibship sizes of all those on the register. Towns and districts with a population rich in the CF gene are mentioned. The number of potential carriers has been determined, so that they can be screened when a practicable detection test is devised. The register has answered a number of questions about CF in southern Africa. It has focused attention on the disease in the region and played a major catalytic role in the formation of the Southern African Cystic Fibrosis Association.