Up to 79% of IBS patients report gastroesophageal reflux disease (GERD) symptoms, and up to 71% of GERD patients report irritable bowel syndrome (IBS) symptoms. There are two principal hypotheses for the common presence of IBS symptoms in GERD patients. The first theory suggests that GERD and IBS overlap in a significant number of patients. The second theory suggests that IBS-like symptoms are part of the spectrum of GERD manifestation. The first theory is supported by genetic studies and similarities in gastrointestinal sensory-motor abnormalities potentially due to general gastrointestinal disorder of smooth muscle or sensory afferents. The other theory is primarily supported by studies demonstrating improvement of IBS-like symptoms in GERD patients receiving anti-reflux treatment. The close relationship between GERD and IBS could be explained by either GERD affecting different levels of the GI tract or a high overlap rate between GERD and IBS due to similar underlying GI dysfunction.