This paper reviews the relationship between mutations in the cystic fibrosis (CF) gene (CFTR mutations) and congenital bilateral absence of the vas deferens (CBAVD). Two CFTR mutations were identified in 14.5% of the 449 man with CBAVD thus far reported in the literature while one CFTR mutation was found in another 48.1%. CBAVD appears to be a heterogeneous genetic condition, many cases being mild forms of cystic fibrosis, others having no relationship with CF. The 5T allele has also been found in 46% of men with CBAVD, but is not associated by the 'classical' picture of cystic fibrosis. The role of the CFTR gene presumably extends beyond a normal development of the vas deferens, possibly playing a role in spermatogenesis. The detection of CFTR mutations in CBAVD had considerable implications in genetic counselling. Couples requesting microsurgical epididymal sperm aspiration/in-vitro fertilization and those in which the man has CF should be offered CFTR mutations screening if CBAVD is the cause of the male infertility.