Abstract Based on clinical studies, the Rome Criteria for the irritable bowel syndrome (IBS) were developed by consensus. The criteria emphasize the presence of abdominal pain and the link between pain and changes in bowel habit. The reliance on a clinical gold standard rather than a biological marker remains one of the major limitations in refining diagnostic criteria. A convincing argument can be mounted that IBS is a disease (a cause of unease). Approximately 10–15% of the general population have IBS, and it affects females more often than males, for unexplained reasons. The annual incidence is probably 1–2%. The onset of symptoms is balanced by symptom loss, so the prevalence remains stable from year to year. Up to one half have symptom improvement over time. Only a minority present for medical care; pain severity as well as psychological distress in part explain health-care seeking. IBS significantly impacts on quality of life. The economic impact is enormous, representing a multi-billion dollar problem in the United States. The development of acceptable, symptom-based diagnostic criteria has advanced the field, stimulating interest in the pathophysiology and targeted pharmacological therapy, which are essential steps if the disease burden is to be reduced.