The majority of men with cystic fibrosis (CF) have associated congenital bilateral absence of the vas deferens (CBVAD). This congenital defect results in the absence of the anatomic ducts through which spermatozoa pass from the testes to the urethra. No spermatozoa are found in the semen, a condition referred to as obstructive azoospermia. This abnormality of the genital-urinary system is associated with the same genetic mutation in the cystic fibrosis transmembrane conductance regulator gene (CFTR ), which leads to the classic presentation of a patient with CF. However, patients may have CBVAD and CFTR mutations without symptoms of CF. Screening for the common mutations may miss a milder rare gene alteration: a DNA variant in the 5T allele. With the advent of assisted reproductive technologies, fertility is now possible for these men. The National Institutes of Health recommend genetic counseling for any couple attempting assisted reproductive techniques when the man has CF or presents with obstructive azoospermia and is positive for a CF mutation.