Most previous studies of the natural history of small colorectal adenomas showed no increase in size, no changes that would have necessitated treatment within a couple of years and that malignant transformation is rare. Using endoscopic follow up for a mean period of 43.1 months we assessed the development and progression of 408 protuberant adenomas that were under 10 mm in diameter. Of the 408 lesions, 22 (5.4%) underwent morphological changes. There were 12 lesions (2.9%) whose final tumor diameter had reached 10 mm or more. There were three lesions (0.7%) that developed and progressed into intramucosal cancer. We concluded from the literature and from our own results that small colorectal protuberant adenomas do not grow to advanced adenomas within 5 years.