The prenatal diagnosis of cystic fibrosis is now routinely performed by using two probes tightly linked to the CF locus (XV2C and KM19). These probes have been shown to exhibit a strong linkage disequilibrium with the CF locus. Our data (103 families) have been pooled with other French data (237 families). They are consistent with the hypothesis of a unique ancestral mutation initially associated with a B (D1E2) restriction fragment length polymorphism (RFLP) haplotype, subsequently reassociated by cross-over with A, C or D haplotypes. Assuming such an hypothesis, the mutation is supposed to be 3000-6000 years old, depending on generation length and the true recombination ratio between the KM19 and CF loci. Up-to-date Spanish, Danish and Greek data are reported together with other previously published population data in order to discuss the geographic origin and age of the mutation in Europe. The action of selection in terms of heterozygote advantage and distorsion of segregation is discussed.