Thirty-one pregnancies in 27 women suffering from mucoviscidosis have been studied in Germany, in the period from 1980 to 1991. This analysis is the largest collection of data to date relating to pregnancy and birth with mucoviscidosis after the American-Canadian study of 1980. The German study demonstrated that only women with few weak symptoms became pregnant: typically the pregnant women's mucoviscidosis was diagnosed at an average age of 9.2 years, and 96.5% of the women had a satisfactory pregravid Shwachman-Kulczicki-Score. Only minor complications were observed in these pregnancies, in particular pulmonary exacerbations (in 18 pregnancies) and an insufficient weight gain (average of 7.2 kg). Abortions were induced in five pregnancies and no spontaneous were observed. There were of maternal deaths during pregnancy or childbirth. More than one quarter of the newborns were premature. All the children had normal sweat chloride test results. 21 women could breast-feed successfully. In fifteen cases the mother's state of health deteriorated after pregnancy however only to a minor (ten cases) or moderate degree (four cases). It is noteworthy that of the twenty six infants twenty one were male. In this study we obtained the unexpected result that unaffected heterocygous children of women with mucoviscidosis are mainly male.