Recurrent abdominal pain has long been acknowledged to be the most common chronic pain entities in children. The purpose of this study is to describe the microbiome in children with FD and to explore relationships between the microbiome and postprandial distress syndrome, anxiety scores, and mucosal biomarkers or anxiety. The specific goals of this study are to: 1) Determine the frequencies and relative proportions for specific bacteria or bacteria phyla in children with FD in both duodenal mucosal specimens and stool samples. 2) Determine if the frequencies or proportions of specific bacteria or bacteria phyla differ between children with and without PDS. 3) Determine bi-variate correlations between bacteria/phyla frequency, bacteria/phyla proportions, anxiety scores, and mucosal biomarkers, respectively.