Irritable bowel syndrome, a very common condition with a high use of health-care costs especially related to diagnostic testing, is traditionally approached by a diagnostic strategy of exclusion. However, data from clinical studies support a positive diagnostic strategy based on symptom-based criteria, absence of alarm signals and, if needed, a few simple blood tests in young patients presenting in primary care. For older patients, and for patients not fulfilling symptom-based criteria or presenting with alarm signals, more thorough investigations are needed, directed by the symptomatology.