The authors analyzed the clinical picture in 18 patients with distal lesion of the colon and an inflammatory focus in the cecum (segmentary lesion), and five patients with distal lesion of the colon revealed with endoscopy and pathomorphological signs of inflammation in visually intact cecum. The analysis shows that in a range of cases the extent of lesion in ulcerous colitis (UC) cannot be determined correctly with colonoscopy. An apparent segmentary character of lesion (inflammation in the distal colon and an inflammatory focus in the cecum) is an additional criterion of unfavorable prognosis of transformation into disseminated UC forms. Such patients need application of the same treatment regimens as in patients with disseminated UC forms.