Patients with extensive ulcerative and Crohn's colitis represent a group at high risk for developing colorectal cancer. Two clear independent risk factors for developing colorectal cancer in patients with chronic colitis include duration and extent of disease. Cancers in chronic colitis do not develop from a colonoscopically recognizable adenomatous polyp similar to that in sporadic colon cancer, but instead arises from flat dysplastic epithelium that is typically not colonoscopically distinguishable from adjacent nondysplastic epithelium. All patients with extensive disease require active management of their increased cancer risk. Active management of cancer risk in chronic long-term colitis should not be presumed to be equivalent to colonoscopic surveillance. There is little data with which to reassure a patient regarding the efficacy of colonoscopic surveillance. A reasonable alternative to colonoscopic surveillance in patients with ulcerative colitis is the restorative proctocolectomy (ileoanal pull-through), which maintains continence and avoids a stoma and appliance. If colonoscopic surveillance is undertaken, a clear understanding of what the definition of a positive surveillance test, ie, when surgical action is taken, is pivotal to the success of the surveillance program. There are now ample data confirming that the finding of any unequivocal dysplasia (low- or high-grade) is associated with a high risk of coexistent or future colorectal cancer. Dysplasia confirmed by a second pathologist (preferably an experienced gastrointestinal pathologist) should prompt a recommendation for colectomy. Future cancer surveillance in chronic colitis will almost certainly involve some applied molecular genetic test.