One-time colonoscopy detects ~25% more advanced lesions (polyps > 10 mm, villous adenomas, adenomatous polyps with high-grade dysplasia, invasive cancer) than one-time FOBT with sigmoidoscopy. Colonoscopy is well suited to screening subjects at high risk, such as those with ulcerative colitis or family predisposition. Perforation rates are 3/1000 for colonoscopy and 1/1000 for sigmoidoscopy. Debate continues on whether colonoscopy is too expensive and invasive for widespread use as a screening tool in standard-risk populations. DRE and barium enema are both insensitive as screening tools.