Irritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by abdominal pain and changes in bowel habits, not sustained by structural changes. There is now consistent evidence indicating that IBS may be the adverse outcome of an acute episode of infectious gastroenteritis, the so-called postinfectious (PI) IBS. The infectious agents involved in the development of PI-IBS include pathogenic bacteria, parasites, and viruses. Abdominal pain and diarrhea are the most common symptoms of PI-IBS. Several studies identified a number of risk factors increasing the susceptibility for PI-IBS development. These include the virulence of the pathogen, the severity, and duration of the acute enteritis, younger age, female sex, and psychological disturbances. Several mucosal abnormalities in the colon or ileum of patients who develop PI-IBS have been described. These changes include increased mucosal permeability, an increased amount of intraepithelial lymphocytes, lamina propria T cells, and mast cells, as well as serotonin-containing enteroendocrine cells. The mediators released by these activated cells may evoke enteric nervous system responses, excite sensory afferent pathways, and induce visceral hyperalgesia. Little is known about the prognosis of PI-IBS, although it is likely better than that of nonspecific IBS. There is little evidence about a specific treatment for PI-IBS. Although probiotics and antibiotics may be promising in the prevention of PI-IBS, the efficacy of these treatments should be assessed in an ad hoc designed study.