The prevalence of urinary stones in a group of subjects living with a permanent ileostomy has been determined by intravenous urography. Thirty-nine of the ileostomists had previously suffered from ulcerative colitis, while the remaining 12 suffered from Crohn's disease. Four of the ileostomists who had had ulcerative colitis had urinary stones (10.3 per cent). These four subjects were all male, so that among the 23 male ileostomists who had had ulcerative colitis 17.4 per cent had urinary stones. No urinary stones were found in the ileostomists with Crohn's disease. Various factors thought to be associated with a liability to urolithiasis have been examined in the ileostomists and also in a control group of 39 healthy subjects matched for age and sex with the ileostomists who had had ulcerative colitis. The ileostomists commonly showed a reduced urinary volume, a low urinary sodium and magnesium content and low urinary pH. The ileostomists were much more prone to be hyperuricaemic than the controls, and hyperuricaemia was strongly associated with the presence of urinary stones.