Calprotectin is a protein especially expressed in neutrophil cytosol. In the last few years, Fecal calprotectin (FC) turned out to be a direct marker of gastrointestinal inflammation. Because of the simplicity of the method, it has been studied in several gastroenterologic diseases but no data are available about its concentration in children with small intestinal bacterial overgrowth (SIBO), a complex and not well known condition defined by an excessive germs proliferation, especially anaerobic, in the small bowel, and characterized by dyspeptic and malabsorption symptoms. The aim of this study was to evaluate FC values in children with SIBO, comparing to healthy subjects, in order to clarify if an inflammatory process coexists with SIBO.We enrolled fifty-eight children affected by SIBO, as diagnosed by Lactulose Breath Test (LBT). They were assessed for FC values on stool samples. We compared them with a control population of 60 healthy children.In SIBO patients, a median value of 36.0 mg/kg and a mean value +/- SD of 43.0 +/- 31.6 mg/kg were calculated, while in healthy controls the median value was 29.5 mg/kg and the mean value +/- SD was 35.7 +/- 20.7 mg/kg, showing no statistically significant differences between the two groups (p = 0.07).FC values are negative in children affected by SIBO, not differing from those obtained in healthy children, suggesting that no subclinical intestinal inflammation involving neutrophils occurs in patients with higher proliferation of bacteria in the small bowel. The presence of high FC levels in children affected by SIBO might not be caused by bacterial overgrowth itself and, in this case, another cause should be investigated.