Saguenay Lac-Saint-Jean (SLSJ), a region located in northeastern Quebec, has a high incidence of cystic fibrosis (CF). During the past few years the majority of the CF patients have been genotyped. The geographical distribution of the birth places of the patients and obligate carriers of the 621 + 1G-->T, the A455E and the delta F508 mutations (which accounted for 89% of the CF chromosomes) showed differences that can be explained by some degree of isolation but also by differential migration. The mean inbreeding and kinship coefficients were higher among the various CFTR mutation groups than in the general population. An ancestor couple common to most of the A455E carriers was identified. These data further substantiate the role of founder effect in the CF population of SLSJ.