Associations between polyps and cancer of the gastrointestinal tract have been fully documented for adenomatous polyps and cancer of the large bowel. The geographic, gender, and age distribution of colorectal adenomas parallels that of colorectal cancer incidence, and individuals with a history of adenomas are at increased risk for metachronous adenomas and cancer. Observational studies of risk factors for incident adenomas have found elevated risk associated with dietary variables including: high fat, low fiber, and low vegetable intake; family history; obesity; smoking; and other exposures, some of which also are associated with cancer. Dietary intervention trials with adenoma recurrence as an endpoint, however, have had little success. Screening with polypectomy has proved effective in reducing cancer incidence and may change the epidemiology of colorectal cancer.