BackgroundIt remains unknown whether the Rome III criteria can exclude organic colonic lesions prior to the diagnosis of irritable bowel syndrome (IBS). We evaluated the colonoscopy results of patients meeting the Rome III criteria for the diagnosis of IBS to determine the presence of organic colonic lesions.MethodsThis study was prospectively conducted at 17 centers in Japan. We enrolled 4528 patients who underwent diagnostic colonoscopy examinations. The diagnosis of IBS was evaluated by questionnaire results according to the Rome III criteria.ResultsWe evaluated 4178 patients (350 were excluded because of incomplete data or previous colonic surgery), of whom 203 met the Rome III criteria (mean age 57.9 years; range 14–87 years) prior to the diagnostic colonoscopy examination. We identified organic colonic diseases in 21 of these 203 patients (10.3 %) , and these disease were also identified in 338 (8.5 %) of 3975 patients who did not fulfill the Rome III criteria. There were no differences in regard to the prevalence of organic colonic diseases between patients who did and did not fulfill the Rome III criteria.ConclusionsThe prevalence of organic colonic diseases in patients who met the Rome III criteria was at an acceptably low level, indicating that the Rome III criteria are adequately specific for the diagnosis of IBS without performing a colonoscopy examination.