Inflammatory bowel disease (IBD) and irritable bowel syndrome share many symptoms. While irritable bowel syndrome is a functional bowel disorder for which no specific treatment is available, the range of effective therapies for IBD is evolving rapidly. Accurate diagnosis of IBD is therefore essential. Clinical assessment, together with various imaging modalities and endoscopy, has been the mainstay of diagnosis for many years. Fecal biomarkers of gastrointestinal inflammation have appeared in the past decade, of which calprotectin, a neutrophil cytosolic protein, has been studied the most. Crohn's disease and ulcerative colitis are chronic remitting and relapsing diseases, and objective assessment of disease activity and response to treatment are important. This review focuses on the use of fecal calprotectin measurements in the diagnosis and monitoring of patients with IBD.