The mean incidence of cystic fibrosis (CF) among North Americans of European ancestry is 1 in 2,500. Studies carried out in different geographic areas report incidence values ranging from 1 in 1,800 to 1 in 8,500, suggesting that incidence has to be assessed specifically for any population. This paper represents the first attempt to evaluate the incidence of CF in Italy and its time-related changes following the discovery of the gene in 1989. Data recorded in the Italian National CF Registry for CF subjects born between 1988 and 2001 were evaluated. All CF patients (1,742) were diagnosed by 1 of 18 specialized CF centers and 7 support services (1-3 in each region) according to the consensus statement on CF diagnosis. The average CF incidence in Italy was found to be 1 in 4,238, which is lower than the values reported elsewhere. The incidence remained nearly constant from 1988 to 2001, although the percentage of subjects screened for CF increased by 44%. Molecular analysis (available for more than 80% of the patients) indicated that the most common mutation (DF508) in Italy occurs in only 49% of CF chromosomes; the other mutations differ from region to region. These differences appeared to be mildly related to differences in reason for diagnosis and type of mutation. Italian registry data supply an incidence of CF lower than that reported for populations of European descent. Part of this difference is probably due to the higher allelic heterogeneity of the CFTR gene in Italy with respect to Northern Europe or the U.S. population of European descent.