Irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) are common, chronic, relapsing, and potentially disabling disorders in the West which are increasing in prevalence in the rest of the world. They typically afflict young adults in the prime of their lives and, consequently, may inflict a considerable emotional, personal, and socioeconomic toll. Not surprisingly, therefore, their management requires considerable clinical acumen and a fundamental commitment to the many dimensions of the patient-doctor relationship. There the similarities end. Despite a considerable body of recent data reporting a number of abnormalities (both upregulation and downregulation) in various components of the mucosal and systemic immune response in IBS, none of these findings come even close to the inflammatory processes that typify IBD. Furthermore, there is little evidence that those with an established diagnosis of IBS (in contrast to those with IBS-type symptoms in which IBD may have been missed (1)) can evolve into IBD; IBS, regardless of immunological or microbiological findings, should not be considered as a part of the spectrum of IBD. If IBS and IBD are distinct entities, then can they co-exist and lead to diagnostic confusion for the clinician?