Serrated polyps of the large intestine, including traditional hyperplastic polyps, traditional serrated adenomas, and more recently described sessile serrated adenomas, have gained increased recognition in recent years because of growing evidence that one of these lesions, the sessile serrated adenoma, might be the precursor lesion for some cases of microsatellite unstable colorectal carcinoma. Nevertheless, there has been some reluctance to embrace the concept of sessile serrated adenoma, and numerous diagnostic challenges exist. This article, which grew out of the Roger C. Haggitt Gastrointestinal Pathology Society Forum presented in Vancouver, Canada, March 6, 2004 as part of the annual meeting of the United States-Canadian Academy of Pathology, reviews the morphologic and molecular evidence for the concept of various polyps in the general category of serrated polyps of the large intestine, in particular the lesion known as the sessile serrated adenoma, and provides a conceptual framework for diagnosis of these lesions.