Irritable bowel syndrome (IBS) is a common chronic functional bowel disorder characterized by abdominal pain or discomfort and alterations in bowel habits. In clinical practice, diagnosis is based on positive symptoms known as the Rome criteria and limited diagnostic screen, taking into account warning features suggestive of organic disease. Minimal diagnostic tests are warranted to rule out structural lesions in a cost-effective manner and to convince the patient of the diagnosis of IBS. An initial diagnosis of IBS is safe and rarely needs revision over time. Persistence of symptoms is to be expected and does not justify suspicion of other diagnoses. Only change in the clinical pattern over time justifies additional investigations. Other diagnostic evaluations depend on predominant symptoms, namely constipation, diarrhea, and pain or discomfort. It should be emphasized that although an initial “positive diagnosis” is safe to exclude other diseases with similar symptoms, a common disorder such as IBS may often coexist with other asymptomatic disorders.