Congenital bilateral absence of the vas deferens (CBAVD) is a form of male infertility in which mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been identified. Cystic fibrosis patients have mutations in both alleles of the gene while most CBAVD patients have mutations in only one allele. Frequently, the second CFTR allele is not mutant but polyvariant. We have studied CFTR gene mutations and polyvariant allele (TG)m(T)n in intron 8 in 37 patients with CBAVD. Ten (27%) compound heterozygotes and 16 (43.3%) heterozygotes have been detected, while no alteration have been found in the coding and intronic bounderies regions in 11 (29.7%) patients. DeltaF508 was the most frequent mutation present in 15/74 (20.3%) alleles. Additional mutant alleles include: R117H (6.8%), R75Q (5.4%), D1270N (2.7%) and G576A (2.7%). We identified in total 14 different mutations and mutant variants, of which one E804V has not been reported previously. Of 37 alleles with not detectable alteration in the coding or splice site regions the (TG)12(T)5 allele has been found in 14 (37.8%) genes. If we consider that (TG)12(T)5 is believed per se to be a highly penetrant pathogenic allele connected with CBAVD, we have detected a disease causing alterations in 49/74 (66.2%) CFTR alleles of CBAVD patients. These results are extremely important for genetic counseling of couples indicated for in vitro fertilization.