Among etiological factors suspected of causing Crohn’s disease a number of bacteria was listed (Yersinia, Mycobacterium kansasi, Mycobacterium pseudotuberculosis) as well as viruses (measles). None of them however can be considered as the only agent. As to external influences, we know the adverse effect of smoking, the toxic effect Al and oral contraceptives. The listed causes may enhance the development of mesenteric thromboses or immunocomplex vasculitis with ischaemization of a certain portion of the small or large intestine with subsequent inflammation. So far we do not know what starts the immunological reaction, but subsequently the process takes place via cytokines, prostaglandin PGE2, leukotriene LTB4 and liberation of free oxygen radicals (this knowledge is applied in therapy). The authors discuss the problem whether Crohn’s disease is one clinical entity with a different course or whether a single diagnosis comprises two or more pathological units.

        Key words: Crohn’s disease, endoscopic diagnosis, ulcerative colitis, cytokines, granulomatous immunocomplex vasculititis, microelements (trace elements), smoking.