Irritable bowel syndrome (IBS) is estimated to affect 10-15% of the U.S population. Recent changes in practice guidelines issued by the American College of Gastroenterology altered diagnostic criteria for IBS to promote more rapid, positive diagnosis without prolonged and invasive testing. While this approach will likely spare many patients time, money and energy, it does raise the possibility that certain conditions that resemble IBS may be missed in the differential diagnosis. Even in patients who have had exhaustive diagnostic workups before receiving their IBS diagnosis, some do not respond to the usual dietary and medical interventions for the condition. RDNs are well positioned to detect clues as to the possibility of IBS-mimicker conditions in their observations of food and symptom interplay and can serve as key partners to MDs in the diagnostic process. This session will review small intestinal bacterial overgrowth, bile acid diarrhea, congenital sucrose isomaltase deficiency (CSID), histamine mediated disorders, systemic nickel allergy and high stool burden related to pelvic floor dysfunction.