It is important to assess the severity of ulcerative colitis (UC) in order to decide the intensity of treatment and predict outcome. The criteria instituted by Truelove and Witts almost 60 years back are still being used. However, they lack a scoring system and offer no clear definition for the moderate group. The criteria with scoring system and endoscopic criteria (Mayo Score) seems to be more useful clinically. Endoscopic assessment is very important and a cautious attempt should always be made even if it enables a limited colonoscopic examination. Proctosigmoidoscopy is advocated at initial stages and after 5 to 7 days. The criteria for severity in general are same for pan-colitis and limited disease.