Introduction: Diagnostic discrimination between inflammatory bowel disease (IBD) and functional gastrointestinal disorders is complex, as they cause similar signs and symptoms. Faecal calprotectin (FC) is a useful marker in this context, and can be used to select patients who will most benefit from colonoscopy. The aim of this study was to evaluate the utility of FC in discriminating between organic disease and functional disorders. Material and methods: The study included 264 patients presenting with gastrointestinal complaints consistent with an organic pathology. FC levels were determined and diagnostic accuracy was assessed using the area under the curve obtained from the final diagnosis. Results: Calprotectin levels in organic bowel disease patients were significantly higher (median 254 mu g/g; 95% confidence interval [CI], interquartile range 105-588.5) than in functional disease patients (95 mu g/g; 95% CI, 47.25-243.92) (P <.0001). Similarly, in patients with IBD, the values obtained were higher (270.85 mu g/g; 95% CI, 96.85-674.00) than in those with irritable bowel syndrome (79.70 mu g/g; 95% CI, 36.50-117.25) (P <.0001). For a cut-off of 150 mu g/g, FC had an area under the ROC curve to discriminate between organic and functional disease of 0.718, and 0.872 to discriminate between irritable bowel syndrome and IBD. Conclusion: Our study supports the importance of FC as a marker in the evaluation of patients with IBD. The best diagnostic accuracy is obtained at a cut-off value of 150 mu g/g. (C) 2016 Elsevier Espana, S.L.U., AEEH y AEG. All rights reserved.