While irritable bowel syndrome (IBS) is common in the West, early studies suggest that the prevalence is low in developing countries. However, recent studies point to increasing prevalence in newly developed Asian economies. The presentation appears to differ from the West, with a lack of female predominance, a greater frequency of upper abdominal pain and defecatory symptoms perceived as being less bothersome. This difference, together with the preoccupation with organic disease, could explain why we may be missing IBS in Asia and also why excess surgery has been observed in some Asian countries. While a recent study from China, consistent with western studies, support an important role for infection and inflammation, early studies from India reporting no association between amoebic infection and IBS appear to dispute this observation. To reconcile these seemingly contradictory observations, an hygiene hypothesis model is proposed. Exposure to a variety of microorganisms early in life could result in the colonization of the intestine with microflora that can respond more efficiently to an episode of gastroenteritis. Together with the changes with evolution of Asian economies such as westernization of the diet and increased psychosocial stress, it is proposed that loss of this internal protective effect, could give rise to a more uniform worldwide prevalence of IBS.