Inflammatory bowel diseases, Crohn's disease and ulcerative colitis, were discovered in the twentieth century. The etiology and pathogenesis has been unsolved until now. At present, three etiological mutually involved factors can be considered. The most important turned out to be the genetics component, which can lead to the chronic inflammation of the bowel. The significant effects of infectious and environmental factors were proven in the pathogenesis of inflammatory bowel diseases. Despite many years elapsed, the "The binary pathogenesis theory of ulcerative colitis", postulated by Maratka in the sixties, can be still accepted.