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Rome III versus Rome IV criteria for IBS 33 2 Introduction Irritable bowel syndrome (IBS) is a functional intestinal disorder characterized by abdominal pain associated with altered bowel habits. IBS has traditionally been subcategorized into four subtypes based on predominant stool pattern: diarrhea (IBS- D), constipation (IBS-C), a mix of diarrhea and constipation (IBS-M) or undefined predominant stool form (IBS-U). IBS is a prevalent disorder worldwide, with prevalence rates of 5-15% in the Western population. 1,2 Symptoms most likely result from complex interactions between several biological, psychological and social factors. 3,4 The exact underlying mechanisms of IBS pathophysiology are however not completely understood and as a consequence accurate non-invasive biomarkers for diagnosis, disease monitoring and treatment evaluation are not available. At present, the diagnosis of IBS is symptom-based, using the Rome criteria. The Rome Foundation, a committee of international experts in the field of functional gastroenterology, has been working on the development and revision of diagnostic criteria for IBS, amongst other functional gastrointestinal (GI) disorders, since 1994. Recently, Rome III criteria (2006) have been updated to Rome IV criteria (2016). Major adjustments include removal of the term abdominal discomfort (Rome III), leaving only the occurrence of abdominal pain as the key requirement for Rome IV criteria. Furthermore, abdominal pain should be present on average at least one day per week in the Rome IV criteria (see Box 2.1 ). 5,6 This new frequency threshold was based on a summary report on the distribution of symptom occurrence rates for all the Rome III symptoms. 7 Most likely, fewer patients will fulfill the new Rome criteria compared to the previously set criteria. Indeed, using Rome IV criteria, a lower population prevalence of IBS has been reported by Whitehead and colleagues. 8,9 Furthermore, IBS subtype identification has been revised, by only taking into account symptomatic stools ( i.e. loose/watery stools and hard/lumpy stools), which might result in a shift in IBS subtypes. 3 Studies on previous editions of the Rome criteria have demonstrated varying IBS prevalence rates depending on the diagnostic criteria employed. Also, differences in patient characteristics and symptomatology have been reported between several criteria. 10-13 As a result of the requirement of weekly symptoms, Rome IV IBS patients are likely to be those with more severe symptomatology and possibly higher prevalence of psychiatric comorbidity and lower quality of life as compared to those fulfilling Rome III criteria. However, data comparing clinical features between Rome III- and Rome IV- IBS populations are still lacking.