-Background -Determination of fecal calprotectin can provide an important guidance for the physician, also in primary care, in the differential diagnosis of gastrointestinal disorders, meanly between inflammatory bowel diseases and irritable bowel syndrome. Objectives -The aims of the present study were to prospectively investigate, in Brazilian adults with gastrointestinal complaints, the value of fecal calprotectin as a biomarker for the differential diagnosis between functional and organic disorders and to correlate the concentrations with the activity of inflammatory bowel diseases. Methods -The study included consecutive patients who had gastrointestinal complaints in which the measurement levels of fecal calprotectin were recommended. Fecal calprotectin was measured using a Bühlmann (Basel, Switzerland) ELISA kit.