The authors report a phenotype-genotype correlation in a population of patients from center and south Italy affected by cystic fibrosis (CF). Thirteen (21%) of patients with pancreatic insufficiency (PI) were homozygous for delta F508, seventeen (27%) were delta F508 heterozygous with an associated unknown allele. Two other described mutations (N1303K, G542X) were also found in a heterozygote status and associated with a severe clinical expression of disease.