Irritable bowel syndrome (IBS) usually is considered a functional gastrointestinal disorder characterized by pain, bloating and either diarrhea or constipation, but a small subgroup of patients report a sudden onset of their IBS symptoms after gastroenteritis, that is named postinfectious IBS. IBS can be diagnosed with confidence when a patient fulfills the Rome II criteria for IBS and displays no warning signs, as determined by a careful history and physical examination. In the past numerous test were considered routine for patients with suspected IBS, however, available data do not support this approach. The etiology of IBS remains unknown and therefore the treatment is focused on relieving symptoms rather than curing the disease. The patient main complaints such as constipation, diarrhea or bloating-pain-gas, determine the therapies of choice, according the severity of them.