Summary points The irritable bowel syndrome affects about 20% of adults in the industrialised world The condition is a disturbance of gastrointestinal function of unknown cause, but abnormalities of intestinal motility and visceral sensation are found in some patients Symptoms of the irritable bowel syndrome are often associated with extraintestinal manifestations, including urinary symptoms, dyspareunia, and fatigue Overall, 40–60% of patients with the irritable bowel syndrome who seek medical advice have psychological symptoms of depression or anxiety, or both Diagnosis of the irritable bowel syndrome can usually be made on the basis of clinical history and examination, but exclusion of organic disease is advisable in patients aged >45 years who present with new bowel symptoms No uniformly successful treatment exists for the irritable bowel syndrome. End organ treatment aimed at relieving abdominal pain (antispasmodic drugs) or disturbed bowel habit (antidiarrhoeal and bulking agents) can produce symptomatic relief, and “central” treatment (for example, anti-depressants, hypnotherapy, psychotherapy) should be considered in patients with associated affective disorders