A higher frequency (25%) of gastrooesophageal reflux (GOR) has been previously reported in patients over 5 years old with cystic fibrosis compared with controls without cystic fibrosis. It was believed that GOR was caused by the complications of cystic fibrosis. We looked for GOR in all 26 children younger than 60 months who had cystic fibrosis diagnosed. They had a classical genetic profile and the usual scattered clinical manifestations for age. GOR was confirmed in 21 (81%): 20 by abnormal pH tracings and in one on a clinical basis. After at least one month of adjusted cystic fibrosis treatment, antireflux treatment (cisapride) was given to 16 patients and variables of GOR improved dramatically. Weight gain was significant and recurrent cough and wheeze disappeared. One year later half of the patients still suffered from GOR. GOR is a major problem in the early life of those with cystic fibrosis and is not the consequence of either respiratory or gastrointestinal complications as it improves with age whereas cystic fibrosis becomes worse with age.