Familial adenomatous polyposis (FAP) leads to adenomas and eventual adenocarcinomas in colon and less frequently, duodenum. Chemopreventive strategies have been studied in FAP patients to delay the development of adenomas and cancers. The non-steroidal anti-inflammatory drugs (NSAIDs) and selective cyclooxygenase-2 inhibitor have shown the regression of colorectal and duodenal adenomas in FAP patients. However, these drugs showed gastrointestinal damage and cardiovascular risks, and new preventive strategies are needed. Metformin, an anti-diabetic drug, has recently been suggested to have a suppressive effect on tumorigenesis via inhibition of mTOR pathway, and have an inhibitory effect on polyp recurrence after removal of sporadic colorectal polyps. In addition, metformin has a number of potential mechnisms of carciovascular bebefit. We devised a randomized, open-label, comparative study to evaluate the effect of combination of celecoxib and metformin on polyps of colorectum and duodenum in FAP patients.