Irritable bowel syndrome is a persistent and relapsing bowel function disorder characterized by defecation associated pain and stool consistency or defecation frequency. This syndrome poses a significant social problem because it is one of the most frequent alimentary tract illness. Etiopathology of the illness is still unclear and appears to be associated with many factors. Among them are bacterial flora, visceral supersensitivity, traumatic event, serotonin dysfunction. To establish diagnosis of irritable bowel syndrome it is necessary to use diagnostic criteria. Nowadays Rome III diagnostic criteria are obligatory. It is necessary to look out for organic illness symptoms or family incidence of colorectal cancer. Despite influence on life quality the illness does not influence life expectancy or does not have complications. Irritable bowel syndrome treatment should be individualized with social status and life quality impact analysis. Pharmacological treatment should be connected with education and psychotherapy in some cases. Irritable bowel syndrome treatment usually consists of 2–3 medicaments and should be aimed at most troublesome symptoms relief. Pharmacological treatment consists of relaxant drugs, 5-HT₃ receptor antagonists, 5-HT₄ agonists, antibiotics, probiotics, antidepressants or psychotropic drugs. Currently clinical trials are performed to test new substances in irritable syndrome treatment.