The traditional diagnostic approach for irritable bowel syndrome (IBS) is to exclude other gastrointestinal conditions, which has led to patients being subjected to excessive testing. However, the development of consensus guidelines, such as Rome III, has enabled physicians to make a positive diagnosis of IBS based on the pattern and nature of symptoms. It is now possible to employ a more rational diagnostic strategy with a reduced need for laboratory testing based on symptom-based approaches aimed at standardizing IBS patient subgroups. Patient outcomes in IBS can be further improved by careful consideration of several diagnostic issues including differentiating between disorders (IBS is 1 of >20 functional gastrointestinal disorders), practical aspects of testing, the indications for colonoscopy, and the need to improve the physician-patient relationship and enhance the patient's adherence to treatment.