Cystic fibrosis (CF) is the most common severe autosomal recessive disease affecting Caucasian population. Genetic linkage studies using DNA markers have allow to map the disease to chromosome 7q31-32. Several of these markers are closely enough to the CF gene, that they can be used for prenatal diagnosis of CF with a high level of confidence. We have studied 100 families with at least one affected individual. Fifteen DNA markers have been used in the present study. 96% of families were fully informatives, and 15 families requested prenatal diagnosis. A total of 17 prenatal diagnosis have been performed in these families between the 8th and the 14th week. Six fetus were diagnosed as affected and eleven as non affected of CF, with a reliability higher than 99% in all cases.