IBS is a common condition, affecting approximately 3% to 15% of the general population based on various diagnostic criteria. There seem to be differences in disease epidemiology between the eastern and the western world. As data from larger Asian epidemiological studies begin to surface,however, such differences appear to be less marked. The proportion of IBS patients who consult a physician for their symptoms is around 50%. Psychological factors and the presence and duration of abdominal pain are all significant predictors for health care seeking. The natural history of IBS is characterized by frequent fluctuation of symptoms and by an overlap with other functional GI disorders, some of which share a number of risk factors for IBS. Unnecessary abdominal surgery is performed in a high proportion of IBS sufferers. Along with the established role for psychosocial conditions in IBS, other risk factors are emerging. Evidence for postinfectious IBS is mounting, but the clinical usefulness of characterizing such patients remains unclear. Food sensitivities are frequently present in IBS, but more well-conducted trials of avoidance diets and desensitization are needed. Finally,genetic markers in IBS are an increasing focus of attention, but the amount of phenotypic variance explained by genetic variability remains to be established.