Evidence points to a significant overlap between irritable bowel syndrome (IBS) and gastroesophageal reflux disease (GERD). In this study, we evaluate this overlap by conducting a systematic review of the literature. Six electronic databases from 1966 through January 2005 were screened by multiple search terms to identify all epidmiological evidence linking IBS and GERD. In addition, AGA meeting abstracts for 2003 and 2004 were also screened. All studies were validated by the authors and data extracted according to predefined criteria. As a separate search strategy, studies evaluating the prevalence of IBS and GERD in the general population were sought. These articles were obtained to compare the prevalence of IBS and GERD in the community to the degree of overlap. The search identified 997 original titles with 15 publications that fulfilled our eligibility criteria. Among the 15 studies, 7 determined the GERD maximum mean prevalence in patients already diagnosed with IBS to be 39.3% and the weighted mean 30.3%. The other 7 studies examined the prevalence of IBS in patients already diagnosed with GERD. The maximum mean prevalence of IBS in subjects with known GERD was 48.8% and the weighted mean 60.5%. Based on the prevalence of IBS (12.1%) and GERD (19.4%) in the community, the rate of IBS in the non-GERD community was calculated to be only 5.1%. There is a strong overlap between GERD and IBS that exceeds the individual presence of each condition. In the absence of GERD, IBS is relatively uncommon.