The development of colorectal cancer is the most serious long-term problem faced by patients with extensive ulcerative colitis and Crohn's colitis, with an incidence 20-fold higher and an average age of onset 20 years younger than colorectal cancer in the general population. This report summarizes the epidemiology, pathology, and recent advances in the molecular pathogenesis of colorectal cancer in inflammatory bowel disease and of its acknowledged precursor, mucosal dysplasia. It also reviews the rationale behind the use of endoscopic surveillance for dysplasia as a means of reducing cancer mortality, as well as some of the issues involved in its effective implementation.