Adequate bowel cleansing is essential for complete examination of the colon mucosa during colonoscopy. Suboptimal bowel preparation has potential adverse consequences, such as missed pathologic abnormalities, the need for repeated procedures, and increased procedure-related complications. Several factors can predict individuals at increased risk for inadequate bowel preparation. If predictors of inadequate bowel preparation are identified, then education should be intensified and a more aggressive bowel regimen recommended. On completion of this article, you should be able to (1) define the frequency of inadequate colon preparations, (2) identify predictors of poor bowel preparation, and (3) use a more aggressive bowel regimen when clinically indicated.