Endoscopic evaluation of mucosal appearance is important for the clinical management of ulcerative colitis patients, as it offers valuable prognostic tools and data useful to change the management and treatment strategies. In the field of severe ulcerative colitis, partial endoscopy and bioptic sampling allows to obtain additional and relevant prognostic information: if severe endoscopic lesions are present, response to standard treatment is less likely, and if CMV superinfection is detected, anti-viral treatment should be added to conventional treatments. When clinical remission is obtained with conventional treatments, distal colonoscopy may add valuable data: the occurrence of complete endoscopic healing is a major predictor of long-term remission with no clinical activity. Finally, biologic treatments, and mainly infliximab, were shown to induce remarkable and significant mucosal healing also in ulcerative colitis, and patients with complete endoscopic healing in response to infliximab were shown to be more likely to experience fewer clinical relapses during the follow-up. Therefore endoscopic evaluation has to be considered a major prognostic marker in ulcerative colitis. In this review data from the Literature supporting this role will be reviewed.