 The study was a randomized, double blind, placebo-controlled, crossover trial conducted at two pediatric tertiary care centers in Naples and Foggia. All children aged 8-17 years referred for IBS or FD to the Pediatric Clinics of the two participating centers between January and December 2014 were eligible for the study. IBS and FD were diagnosed using the Rome III criteria for pediatric FGIDs. The main exclusion criterion was the presence of chronic organic gastrointestinal diseases, assessed by full clinical history and examination, and initial laboratory investigation including complete blood cell count, erythrocyte sedimentation rate, C-reactive protein, serum amylase and lipase, tissue transglutaminase antibodies, total serum immunoglubulins A, and fecal calprotectin. Abnormalities in any of these tests resulted in the patients exclusion from the study. Further exclusion criteria were previous abdominal surgery, diseases affecting bowel motility, or concomitant psychiatric, neurological, metabolic, renal, hepatic, infectious, hematological, cardiovascular or pulmonary disorders. Finally, patients who had been using any commercial preparation of probiotics during the previous 3 months were also excluded. 