Inclusion Criteria:  Ulcerative Colitis confirmed by endoscopy and histology. Involvement 30% of the colonic surface (or any extent if concomitant with PSC). Duration of the disease >7 years (or any duration if concomitant with PSC).  Exclusion Criteria:  Personal history of colorectal cancer or high-grade dysplasia. Previous colectomy (partial or complete). Coagulopathy that prevents biopsies or polypectomy. Colonoscopy performed in the previous 6 months. Pregnant or nursing women. Inadequate bowel preparation. Presence of endoscopic Ulcerative Colitis activity. Colonic stenosis and incomplete colonoscopy.