OBJECTIVE: To review the pathophysiology in order to explain the clinical manifestation and treatment of this syndrome, which has not been completely explained yet. METHODS: References were searched on recent review articles, personal files, and Medline. RESULTS: Irritable bowel syndrome in children or chronic nonspecific diarrhea is a very frequent reason for pediatric gastroenterology visits. It is a benign disease and disappears with age, but may cause extreme worry to parents. The pathophysiology is still unclear, and there is not laboratory corroboration. Thus, it is frequently diagnosed incorrectly, although it has proper clinical manifestation (if there is no diet or medicine manipulation). Dietary advice is usually efficient, and is based on pathophysiologic data. The use of drug is still discussed. CONCLUSIONS: Irritable bowel syndrome must be always considered in oligosymptomatic children without signs of malnutrition, with diarrhea, between 6 months and 5 years of age. Drugs are not necessary, and their action is still unclear. Food manipulation based on pathophysiology is enough.