Genetic counseling is an important part of health care in patients with cystic fibrosis or respiratory diseases associated with the CFTR (cystic fibrosis transmembrane conductance regulator) gene, including certain types of allergic bronchopulmonary aspergilloses or bronchial diseases (diffuse bronchiectasia). The basic goal is to provide patients with information on the transmission of cystic fibrosis and to asses the risk of recurrence. This risk is determined from molecular biology analyses examining the CFTR gene. Genotyping is the only means of screening for the heterozygous state, frequent in the French population (about 1/30). Because of the large number of mutated alleles not covered entirely by the genetic tests, there remains a question of probability expressed as a residual risk of a heterozygous state. A prenatal genotype diagnosis should be proposed to heterozygous couples who have a 25% risk of having a diseased child. Technically, this is almost always possible and the results are highly reliable. Nevertheless, there remains the risks related to sample taking and the ethical issue about which the patients must be informed. Management of these at risk couples who desire a child must be based on a multidisciplinary approach, particularly important when one of the parents has overt cystic fibrosis.