Flexible sigmoidoscopy remains a common tool used for the periodic screening of colorectal cancer. Most organizations recommend screening at three- to five-year intervals beginning at age 50 for persons with average risk. Extensive training in endoscopic maneuvering, colorectal anatomy and pathologic recognition is required. Most physicians report comfort performing the procedure unsupervised after 10 to 25 precepted sessions. The procedure involves the insertion of the sigmoidoscope through the anus and distal rectum and advancement of the scope tip to an average depth of 48 to 55 cm in the sigmoid colon. Once the sigmoidoscope has been appropriately advanced, the scope is slowly withdrawn, allowing for the inspection of colon mucosa during withdrawal. Polyps less than 5 mm in diameter should be biopsied. Polyps 5 to 10 mm or greater can be assumed to be adenomatous, and follow-up colonoscopy for complete polypectomy is required. Diverticulosis, hemorrhoids, nonspecific colitis and pseudomembranes may also be encountered during inspection. Use of preprocedural benzodiazepines can be helpful in reducing patient discomfort. 2001;63:1375-80,1383-4,1385-8.)