Gastro-oesophageal reflux (GOR) occurs frequently in children with cystic fibrosis (CF) but has not been studied in adult CF. We surveyed such symptoms by structured questionnaire in 50 adult CF patients (mean age 26 years, range 16-50; 24 male) and performed oesophageal manometry and 24-hour pH recording in 10 who had reflux symptoms (mean age 28 years, range 21-35; 8 men). 47 patients (94%) had upper gastrointestinal symptoms: 40 (80%) heartburn (27 worse when supine); 26 (52%) regurgitation; and 28 (56%) dyspepsia. At oesophageal manometry, lower oesophageal sphincter barrier pressure (LOSBP) was subnormal in 6 of the 10 patients and 3 had uncoordinated peristalsis in the mid oesophagus. 8 patients had raised DeMeester scores, indicating significant GOR. Those patients with a LOSBP < 5mm Hg had a higher DeMeester score (mean 81.0, range 47.9-128.8) than the patients with a normal LOSBP (26.9, 8.7-56.5; p < 0.002). These results show that adult CF patients have high rates of GOR symptoms, diminished LOSBP, and acid reflux.