The frequencies of DF508, the main cystic fibrosis mutation, vary among different populations in Western Europe; they are higher in northwestern Europeans than in southeastern populations. Our new analysis is based on results from 66 different laboratories on 17,886 cystic fibrosis chromosomes (from 70 locations and 26 countries). The correlation between DF508 frequency values and cystic fibrosis incidence is calculated in the corresponding groups.