Because irritable bowel syndrome (IBS) is a prevalent cause of visits to the gastroenterologist, it is extremely important to have accurate guidelines for the diagnosis. During the clinical assessment of IBS, the physician must look for the gastrointestinal symptoms, extraintestinal symptoms, and psychological history that are commonly associated with IBS. There are three diagnostic criteria that may be used in the IBS diagnosis: Manning, Rome I, and Rome II. Although there is discrepancy about which is most effective, we recommend that the Rome II be used in clinical practice. To confidently diagnose IBS, the physician must rule out organic disease as a cause of symptoms. This can be done by evaluating the patient's symptoms and screening for "red flags." The diagnostic strategy for IBS involves a thorough evaluation of the patient: taking a patient history, performing a physical exam, and performing the appropriate diagnostic tests when necessary.