In the past two decades, medical opinion has changed regarding how to diagnose IBS. The older view emphasized that IBS should be regarded primarily as a “diagnosis of exclusion;” that is, diagnosed only after diagnostic testing excludes many disorders that could possibly cause the symptoms. Fortunately, physicians can now diagnose IBS in most patients by recognizing certain symptom details, performing a physical examination, and undertaking limited diagnostic testing. This simpler approach is grounded on recent knowledge…and it leads to a reliable diagnosis in most cases. Revised and updated 2009.