The risk of colorectal cancer in patients with long-standing ulcerative colitis or colonic Crohn's disease is increased. Patients with long-standing ulcerative colitis are offered enrollment into programs of endoscopic surveillance. Although direct evidence for a protective effect of surveillance against death from colorectal cancer is limited, colorectal cancer is detected at an earlier stage and the corresponding prognosis is better. Targeting biopsies using pancolonic chromoendoscopy is superior to taking multiple random biopsies for the detection of dysplasia at colonoscopy.