The effect on bladder function of protectomy for colitis or Crohn's disease was studied by means of a questionnaire and by pressure/flow cystometry. Thirty-seven patients who had undergone protectomy for inflammatory bowel disease were compared with 34 control patients who had undergone bowel resection without protectomy. Symptoms of urinary dysfunction were found to be significantly more common in patients after protectomy than in controls (P less than 0.05). Straining at micturition (P less than 0.05) and a sensation of incomplete emptying of the bladder (P less than 0.02), in particular, were significantly more common after protectomy. Evidence of denervation of the bladder, as shown by the finding of capacious bladders with poor detrusor function, was found in 6 patients after protectomy but in none of the controls (P less than 0.05). The residual volume of urine in the bladder after micturition was significantly greater in patients after protectomy than in controls (P less than 0.02). Thus, the bladder is at risk of denervation in the course of protectomy for inflammatory bowel disease even when dissection is kept close to the rectum.