The irritable bowel syndrome (IBS) is a common chronic functional disorder. Although its cause is unclear, a multifactorial etiology has been hypothesized with several putative pathophysiological mechanisms which may interact. These include abnormal intestinal motor function, abnormal visceral perception, psychosocial factors and luminal factors that irritate the small bowel and colon. A positive diagnosis should be made from an accurate history and physical examination and requires confirmation by exclusion of structural, metabolic and infectious processes that may result in similar clinical presentations. The IBS can be classified on the basis of its broad clinical spectrum of severity and variable patterns of dominant symptoms. Such a classification permits an appropriately graduated treatment approach that includes patient education, dietary adjustment, psychotherapeutic and behavioral techniques, as well as a symptom-orientated pharmaco- and psychopharmacotherapy. The majority of patients has mild symptoms and requires no specific treatment besides careful education and reassurance and dietary adjustment. For moderate symptom severity, additional psychotherapy and behavior techniques are indicated, which should be combined with pharmacotherapy targeted at the presumed pathomechanism. For severe symptoms, physician-based behavior modification and psychopharmacological agents may be needed.