Background: Distinguishing between inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) can be challenging. Aims: To investigate the utility of faecal lactoferrin (LF) as a marker of inflammation in patients with IBD, IBS and controls. Methods: Disease activity in IBD patients were assessed using the modified Harvey-Bradshaw Activity Index. Stool samples were analysed using an ELISA assay. Results: 137 patients with IBS, 126 ulcerative colitis (UC) and 104 Crohn's disease (CD) and 98 healthy volunteers were recruited. The median ± IQ LF concentration (ug/g faecal weight) was 0 ± 1.4 for IBS patients, 6.6 ± 42 for UC patients, 4 ± 12.7 for CD patients and 0.5 ± 2 for healthy controls. LF levels were significantly higher in IBD patients compared to IBS/healthy controls (p<0.001). The median LF concentrations were significantly higher in active UC & CD patients compared to inactive patients ((p<0.001 and p=0.002 respectively). The sensitivity, specificity, positive and negative predictive values of LF in distinguishing active IBD from IBS/healthy controls was 67% and 96%, 87% and 86.8% respectively. Conclusion: LF is useful to differentiate between IBD and IBS and can be used as an adjunct to blood parameters to determine IBD patients who have ongoing inflammation.