A higher prevalence of cystic fibrosis transmembrane regulator (CFTR) gene mutations has been suggested both in men affected by congenital aplasia of the vas deferens, and in individuals presenting with reduced sperm quality. In this case, an increased risk for offspring being affected by cystic fibrosis (CF) can be expected in couples who are planning to undergo intracytoplasmic sperm injection (ICSI), since most of the male partners suffer from infertility. In order to determine the risk for these couples more precisely, we offered them a test for the most frequent CF mutations prevalent in the German population. The frequency of mutations within the CFTR gene in the female group was in the same range as expected for the general population (six out of 150). In 10 out of 207 males tested, infertility could be explained by exogenous factors not related to CFTR. Among the remaining 197 males with idiopathic infertility, we detected 13 heterozygotes for a mutation within the CFTR gene. This slightly, but significantly (P = 0.014), elevated rate could indicate that infertile males have, compared with the general population, an increased risk of being a carrier of a CFTR gene mutation.