The etiology of ulcerative colitis remains unknown. The principal hypothesis have included infection, allergy to dietary components, inmune responses to bacterias or self antigens, the possibility of abnormalities in the epithelial cell and genetic susceptibility. It is also possible that immunologic mecanisms within the colonic lamina propria are involved in the pathogenesis affecting both humoral and cellular responses. Genetic factors seems to play an important role as evidenced by the increased incidence among several members of the same family. It seems likely that several genes are involved in determining susceptibility to the disease. There are not important advances in the field of medical therapy after the introduction of steroids, inmunomodulators, salycilates and ciclosporyn.