•Gastrointestinal symptoms are experienced by the majority of CF patients.•Oro-caecal transit time was 2 h longer in CF than controls.•Absent postprandial drop in small bowel water suggests partial ileal obstruction.•Using MRI as an endpoint may facilitate future gut research in CF. Cystic fibrosis (CF) is a multi-system genetic disorder affecting >72,000 people worldwide. Most CF patients experience gastrointestinal symptoms and can develop complications. However, the mechanisms of CF gut disease are not well understood. We evaluated gut function and transit in CF using magnetic resonance imaging (MRI). We hypothesised oro-caecal transit time (OCTT) is longer in CF; with lower small bowel water content (SBWC). Twelve CF patients aged 12–40 years and 12 age and sex-matched controls underwent serial MRIs over 1 day with standardised meals. The primary endpoint was OCTT, assessed by the appearance of a food bolus in the caecum. Other measures included corrected SBWC and corrected colonic volume (both area under the curve, AUC), gastric half-emptying time and gastrointestinal symptoms. OCTT was longer in CF (CF 330 mins 270, >360 vs. controls 210 mins 173, 315, p = 0.04), with no difference in gastric half-emptying times. Corrected SBWC was higher in CF (CF 62 L.min/m2 36, 80 vs. controls 34 L.min/m2 28, 41, p = 0.021); minimal postprandial decrease between T240 and T300 (CF 13 mL/m2 -13, 57 vs. controls 102 mL/m2 67, 108, p = 0.002) suggests impaired ileal emptying. Corrected colonic volumes were higher in CF (CF 186 L.min/m2 167, 206 vs. controls 123 L.min/m2 89, 146, p = 0.012). There were no differences in gastrointestinal symptoms. MRI provides novel insights into CF pathophysiology. Sub-clinical ileal obstruction may be more prevalent than previously thought. Gastrointestinal MRI shows promise as an investigational tool in CF. Display omitted