Cystic fibrosis (CF) is the most common autosomal recessive disease in Caucasians. In 97-98% of men with CF, bilateral congenital absence of the vas deferens (CBAVD) blocks the transport of spermatozoa resulting in azoospermia. Abnormalities in sperm parameters have also been identified in males with CF. To date, over 800 disease-causing mutations of the CF transmembrane conductance regulator (CFTR) gene have been identified (also called ABCC7). Current legislation suggests that prior to intracytoplasmic sperm injection (ICSI) treatment, men with CBAVD or unexplained oligozoospermia should be considered for screening. If the male is negative with routine screening then the female partner is not screened. This is fundamentally wrong because if the female is screened and is found to be CF positive on routine testing, her partner would then need the fullest possible investigation of the CFTR gene. It is ideal to screen both partners in cases of oligozoospermia. However, if the resources are stretched, then only the female needs to be routinely screened because if she is negative, then the couple's residual risk of having a CF or CBAVD child will be reduced to 1:960. Only when the female is found to be a carrier does the male partner need routine screening followed by full testing for known mutations.