In the US, the cumulative lifetime risk of developing carcinoma of the upper gastrointestinal tract is less than 1 per cent, premalignant conditions are uncommon, and esophageal and gastric malignancies are rarely curable even when identified early. Endoscopic screening of the upper gastrointestinal tract in asymptomatic persons thus cannot be justified. Surveillance of persons with certain uncommon conditions associated with a higher risk of upper gastrointestinal cancer may be of benefit. These conditions include achalasia, Barrett's esophagus, chronic atrophic gastritis with intestinal metaplasia, familial polyposis coli, gastric polyps, lye stricture, Plummer-Vinson syndrome, and tylosis. In the lower gastrointestinal tract, however, the lifetime risk of developing carcinoma is 5 per cent, premalignant conditions and lesions are common, and carcinoma is curable when detected at an early stage. Sigmoidoscopic screening of asymptomatic adults has been advocated by the American Cancer Society but has not become widely practiced because of its cost, required physician effort, low overall yield, and poor patient compliance. Surveillance by flexible sigmoidoscopy is recommended for persons at slightly increased risk of colorectal carcinoma who have prior breast or gynecologic malignancy or a family history of colorectal malignancy. Colonoscopic surveillance is recommended for patients with high risk of colorectal cancer who have had prior colorectal carcinoma or adenoma or who have inflammatory bowel disease or a ureterosigmoidostomy.