As colorectal cancer screening gains acceptance by the public, the use of colonoscopy will increase. The frequency of surveillance examinations after detection of an adenoma is one of the largest contributors to the cost of colorectal cancer screening. Ten years after the publication of the landmark National Polyp Study, the issue of when to perform surveillance examinations and how often to expect advanced findings remains acute. Current guidelines for surveillance vary across specialty organizations. Individuals with advanced adenomas are at increased risk for recurrent advanced adenomas. The impact of multiple nonadvanced adenomas or a single nonadvanced adenoma on subsequent risk of an advanced adenoma or cancer is less clear. Still less is known about findings on repeat examinations after an initial negative examination, whether after colonoscopy or sigmoidoscopy. The yield after a negative examination is an important consideration in determining the recommended interval for screening colonoscopy. For example, the data supporting a 10-yr interval for screening colonoscopy is only indirect. What little we do know about the yield after negative examinations comes from selected, nonrepresentative populations. Of concern, evidence from several polyp prevention trials demonstrates higher yields for subsequent cancer than would be expected, despite a relatively high use of surveillance procedures in follow-up. Further population-based research on the frequency of use and yield of surveillance examinations is needed. Studies that examine the need and the needed timing of subsequent surveillance are essential to containing costs for screening as well as to informing the public better about what endoscopic screening can and cannot accomplish.