The histological activity of the bowel inflammation is an extremely important morphological criterion that is encountered in the diagnosis of colitis. However, the determining of its degree is subjective and still does not have a generally accepted principle of gradation. The article describes the most common scale-schemes for assessing the severity of colitis, that include the degree of microscopic changes. The results of the analysis of the of histological activity degree on the material of colonobioptates in colitis of various etiologies (467 patients) are presented. It has been shown that the Geboes scale of ulcerative colitis can be used to assess histological activity in all forms of colitis. The histological features of inflammation should be reflected in the pathological diagnosis and are essential for clinical decision making. This index allows for a comparative analysis of clinical, endoscopic and morphological parameters and better control of the patient’s condition during the treatment.