The diagnosis of irritable bowel syndrome (IBS) remains a diagnosis of exclusion, whereby an extensive investigation is performed to exclude other organic diseases that may explain the symptoms of patients. Attempts to have a positive diagnosis based on symptom assessments failed to achieve widely use in clinical practice. Abnormalities in the gastrointestinal endocrine cells in IBS patients have been reported recently, providing evidence that IBS is an organic disorder, and opening the door to the use of these abnormalities as markers for a positive diagnosis of IBS. New and promising drugs for the treatment of IBS with constipation as the predominant symptom are currently on the market, and the treatment results have been satisfactory thus far.