OBJECTIVE: To investigate the effects of ileum resection in orthotopic neobladder construction on gastrointestinal function and metabolic control. MATERIAL AND METHODS: We included 28 patients who underwent radical cystectomy and construction of an orthotopic neobladder or continent ileal reservoir for bladder cancer. As controls, 10 patients endoscopically treated for non-invasive bladder cancer (TaG2) were enrolled. Gastrointestinal symptoms, enterohepatic bile salt circulation, gastric emptying and gastrointestinal hormones involved in metabolic control were monitored. RESULTS: Of the cystectomy patients, 25% experienced daily diarrhoea and faecal urgency due to bile acid malabsorption, compared to 0% of the controls (p = 0.013). The cystectomy patients experienced faster gastric emptying and had higher levels of peptide YY. Plasma concentrations of insulin, glucagon-like peptide-1 and glucose were unchanged. CONCLUSIONS: Using the distal ileum for orthotopic neobladder construction causes bowel disorders in a quarter of cystectomy patients. Diarrhoea and faecal urgency are probably caused by decreased reabsorption of bile and are not due to changes in gastrointestinal hormones. A sizeable proportion of patients develop bile salt-induced diarrhoea, which can be relieved by treatment with cholestyramine.