Postinfective irritable bowel syndrome with diarrhoea and idiopathic bile acid malabsorption remains an enigma. We examined the records of 84 patients whose 75SeHCAT scans were indicative of bile acid malabsorption (< 15% one week retention). Identifiable causes of bile acid malabsorption were: previous ileal surgery (7), Crohn's disease (22), radiation enteritis (13), vagotomy, gastrectomy or cholecystectomy (10) and miscellaneous (3). Sixteen of 29 patients with apparently idiopathic bile acid malabsorption gave a clear history of acute gastroenteritis before the onset of chronic diarrhoea lasting from 0.25-18 years until their positive 75SeHCAT scan. Only four cases of campylobacter, and one each of shigella and salmonella were documented. Extensive investigation failed to detect other possible pathologies. In response to bile acid sequestrants, mean stool frequency fell from 7.2 per day to 2.1 per day (p < 0.001). We have observed that postinfective chronic diarrhoea is associated with chronic bile acid malabsorption, which can be successfully treated with bile acid sequestrants such as cholestyramine.