Introduction: Acute infectious diarrhea is one of the most common diseases worldwide. Procalcitonin (PCT) is useful for antibiotic stewardship in lower respiratory tract infections but has been poorly studied in infectious diarrhea. Our objective is to describe the PCT concentrations according to diarrhea etiology. Methods: This is a single-center prospective cohort study involving adults consulting the emergency department (ED) for an acute diarrhea or colitis. Serum PCT was measured and a stool sample was tested with FilmArray® Gastro-Intestinal Panel. The primary endpoint is the PCT concentration according to each type of pathogen identified using Gastro-Intestinal-panel and/or stool cultures at ED admission. Results: 125 patients were included: 80 had an acute infectious diarrhea, 21 an acute colitis and 24 another illness causing diarrhea. The median (interquartile ranges) PCT values (ng/ml) were 0.13 (0.08-0.28), 0.07 (0.06-0.54), 0.13 (0.09-0.26) and 0.05 (0.03-0.17), respectively if there was a bacteria (n=41), parasite (n=3), virus (n=10) or no pathogen identified and 0.34 (0.13-1.03) if the diarrhea was due to another illness (n=24). Conclusion: In patients admitted to the ED with an acute infectious diarrhea or acute colitis, PCT remained low when a bacteria was identified. It may not be informative in current practice to guide antibiotic therapy.