Three intragenic microsatellites of the CFTR gene, a TA and a CA repeats, namely IVS17bTA and IVS17bCA, located in intron 17b and a CA repeat (IVS8CA) located in intron 8 of the CFTR gene, were analyzed in a large sample of Italian cystic fibrosis (CF) and normal chromosomes. Linkage disequilibrium was evaluated between each marker and difference CF mutations on a total of 377 CF and 358 normal chromosomes. Our results are consistent with the hypothesis that all delta F508 chromosomes derive from a single mutational event. The same hypothesis is valid for mutations G542X, N1303K, 1717-1G-->A, which might have been originated more recently than delta F508.