We studied the influence of genetic counseling for cystic fibrosis on family planning, using neonatal screening, family size at time of diagnosis, and maternal age as possible determinants for reproductive behaviour. The expected number of children born to mothers of equal age and parity in the same period was approximated on the basis of population statistics. These numbers were compared to the numbers of children born in the study group after a CF diagnosis and information on the 25% recurrence risk were given. A 50.8% reduction in childbirth was found in the study group, although 77% of families had decided against further high-risk pregnancies. No statistically significant influence of neonatal screening could be demonstrated, but this may be due to the small number of families involved.