To determine the degree of agreement of Rome III and Rome II criteria in diagnosing irritable bowel syndrome (IBS) and to compare the clinical difference between the patients diagnosed with these two criteria.3014 patients in the gastrointestinal outpatient department were enrolled consecutively and interviewed face to face with a standard questionnaire.(1) 480 patients were diagnosed as IBS with Rome III criteria. The overall detection rate was 15.9% (480/3014). The proportion of IBS subtypes was as follows: IBS with constipation 27.9% (134/480), IBS with diarrhea 32.7% (157/480), Mixed IBS 6.7% (32/480), Unsubtyped IBS 32.7% (157/480). No difference was observed between different sex and age groups; with Rome II criteria, 558 patients were diagnosed with a detection rate of 18.5% (558/3014). The proportion of IBS subtypes was as follows: constipation predominant IBS 33.2% (185/558), diarrhea predominant IBS 38.2% (213/558), others 28.7% (160/558). The detection rate was higher in female patients (P = 0.002), but there was no difference between different age groups. The detection rate of Rome III criteria was lower than that of Rome II criteria (P = 0.008). There was a good accordance between these two criteria in the diagnosis of IBS (P D-IBS > U-IBS, P < 0.005) while no difference was observed on the abdominal symptoms and the healthcare seeking rates in the last 3 months.There is a good accordance between Rome II and Rome III criteria in diagnosing IBS. Compared to Rome II criteria, Rome III criteria has a lower detection rate. It is more practical in the clinical practice with clear definition of symptom frequency and easy way of subtyping IBS. The patients diagnosed with Rome III criteria had more severe symptoms and higher healthcare seeking rate, they are more suitable for clinical trial.