The case records of 11 patients with cystic fibrosis (CF) who had 13 completed pregnancies between 1975 and 1995 were retrospectively reviewed to assess: (1) the changes in spirometry and body mass index (BMI) during pregnancy; and (2) maternal and neonatal complications and outcomes. Prepregnancy the mean age of the group was 24 (range 17-27) years. Two patients were exsmokers, 7 had pancreatic insufficiency and 7 had chest X-ray evidence of bronchiectasis. None of the patients had diabetes mellitus but 3 developed gestational diabetes. The mean +/- SEM (% predicted) forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) prepregnancy were 2.3 +/- 1.0 (83%) litres and 3.0 +/- 0.9 (85%) litres respectively. Five patients had normal spirometry (FEV1 and FVC >80% predicted) prior to 6 pregnancies. The mean body mass index (kg/height(m)2) for the group was 20.5 +/- 2.0. There was a significant decline in spirometry during pregnancy (FEV1 15.5 +/- 6.6% p<0.01; FVC 14.0 +/- 8.3% p<0.5). However, FVC but not FEV1 recovered to prepregnancy values by 12 months postpartum. There was a significant increase in both weight (7.1 kg) and BMI (2.6 kg/height(m)2) at the time of delivery compared with prepregnancy (p=0.0004). However, postpregnancy both weight and BMI had returned to their prepregnancy values (p<0.2). Mothers with an FEV1>80% had less decline in FEV1 related to pregnancy, better outcomes, fewer operative and instrumental deliveries, fewer preterm infants and fewer neonatal complications. Suggestions for the planning and management of pregnancy in women with CF are discussed.