The syndrome diagnosis 'irritable bowel syndrome' (IBS) is often made on the basis of exclusion, but the question is how many diagnostic tests should be performed in order to establish this diagnosis with a degree of confidence. We present the diagnostic value of various IBS criteria for excluding IBS, based on a systematic review. The potential of the various criteria for distinguishing IBS from organic disease is extremely variable and disappointing. Patients fulfilling IBS criteria have, however, a lower risk of organic disease than patients with abdominal symptoms who do not fulfil the criteria. The same holds true for the diagnostic performance of individual alerting symptoms. These seem to be present frequently in IBS patients in whom there is no underlying organic bowel condition. An organic condition cannot be accurately excluded on the basis of symptom criteria. However, the low prior risk of organic conditions among patients who consult a primary care doctor and who meet IBS criteria argues against exhaustive diagnostic evaluation.