Although the first observations of gastrointestinal symptoms associated with morphological lesions were made by Sir William Osler as early as 1892, the last decade was when the research on aetiology of irritable bowel syndrome (IBS) emerged. Especially the infective background deserves attention. Intestinal pathogens such as Enterobacteriaceae are known to provoke enterochromaffin cells' hyperplasia, leading to production of excess amounts of serotonin, and diarrhoea, the most common symptom of IBS, then follows. Especially people with SERT gene mutations are at risk. Patients with IBS undergo laborious diagnostic workup in order to exclude cancer, especially of the gastrointestinal tract. Treatment consists of well established modalities (diet, pharmacotherapy), and one should not forget antimicrobial prophylaxis during travels to areas with poor hygiene levels.