SUMMARYBackground: Inflammatory bowel disease is a risk factor for gall-bladder stones, but there is controversy about the composition of these stones and whether such patients develop lithogenic bile. Methods: In 54 gallstone-free inflammatory bowel disease patients and 13 non-inflammatory bowel disease patients with cholesterol-rich gallstones, we measured the biliary cholesterol saturation indices, nucleation times and bilirubin concentrations, and determined the bile acid composition and molecular species of phosphatidylcholine, in gall-bladder bile. Results: Patients with Crohn's colitis or ulcerative colitis had less saturated bile (mean cholesterol saturation index, 0.9) and longer nucleation times (median,