Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are a relatively frequent cause of male infertility such as congenital absence of vas deferens. This finding suggests that CFTR could play a significant role in the etiopathogenesis of congenital absence of vas deferens.To assess how often CFTR mutations and 5-thymidine variant of the polythymidine tract of intron 8 are detected in congenital absence of vas deferens we selected 35 infertile male adults caused by congenital absence of vas deferens.Frequency of mutations differs significantly from that in the general population (2% vs 40% respectively) and the delta F 508 mutation accounts for 35% of these mutations. Abnormal sweat test resulted in several patients with a mutation than in others and this difference was highly significant.This result confirms the role of CFTR protein in the pathogenesis of this malformation and suggests that CBAVD phenotype can represent a mild form of cystic fibrosis. Consequently genetic analysis should take into account the presence of an associated mutation and patients with bilateral agenesia and their partners should be screened for cystic fibrosis prior to any in vitro fertilization techniques.