Probiotics are live bacteria administered orally, successfully used in children with acute gastroenteritis, as well as in preventing and treating atopic diseases in children. In addition, probiotics have been used as adjuvant therapy in patients with pouchitis and inflammatory bowel diseases. Interestingly, probiotic supplementation is able to reduce the incidence of fever, child care absences, antibiotic prescription and to prevent nosocomial gastrointestinal and respiratory infections. The effect of probiotics may be through improvement of intestinal barrier function and modulation of immune response. The latter mechanism could well explain the clinical effects of probiotics observed in extraintestinal diseases.