In 1984, we interviewed 105 Belgian families with a Cystic Fibrosis (CF) child in order to assess the impact of the birth of their CF-child on subsequent family planning and to evaluate their attitudes towards prenatal diagnosis. Three years later, in 1987, they received a mailed questionnaire for an updating of the reproduction data and to assess their knowledge and intentions with regard to the new possibilities of DNA diagnosis. The birth of a CF-child had a major impact upon subsequent family planning. This effect was found both in the reproductive plans reported by the parents and in the occurrence of pregnancies during the follow-up interval. This effect can be attributed mostly to the recurrence risk and consists of postponing pregnancies as well as of deciding against further offspring. If the CF-child was the firstborn, the chance of having another child was greater than if there was already a healthy child before the birth of the CF-child. Nevertheless, only 47% of the families in which the CF-child was the firstborn, and who could be followed for an average period of 7 years, had another pregnancy. A large majority of families intended to use prenatal diagnosis should a pregnancy occur. In half of the pregnancies that occurred between 1984 and 1987, a prenatal diagnosis was performed. On the other hand, there is less consensus about pregnancy interruption should prenatal diagnosis reveal an affected fetus.(ABSTRACT TRUNCATED AT 250 WORDS)