Although the cumulative prevalence of colorectal cancer among patients with ulcerative colitis is similar to that among patients with sporadic colorectal cancer, the younger age of ulcerative colitis patients with cancer accounts for the age-specific relative risk. Approximately half of ulcerative colitis patients with colorectal cancer die from metastatic disease. Pancolitis of long duration and coexistent primary sclerosing cholangitis are strong risk factors for cancer that should prompt entry into cancer surveillance programs. When done appropriately, cancer surveillance in patients with inflammatory bowel disease can be very effective, and at a reasonable cost.