Epidemiological evidence indicates a link between obesity and human colon cancer. A putative association between obesity and colon tumorigenesis has been explored experimentally using chemical carcinogens administered to obese rodents. The main objective of this study was to generate a new mouse line that displays both obesity and intestinal tumorigenesis. To this end, we have generated C57BLKS-mLepr db/db ; Apc 1638N/ þ mice combining both db and Apc mutations. The db mutation results in obesity and type 2 diabetes, the Apc mutation is a key initiating event of intestinal neoplasia. All mice were euthanized at 6 months of age and all regions of the gastrointestinal tract examined for tumors. The results show that the combination of Apc 1638N/ þ and db mutations not only enhanced mutant Apc-driven small intestinal tumorigenesis but also induced gastric and colonic tumors. Homozygous db mice did not develop gastrointestinal neoplasia. These findings indicate that obesity associated with type 2 diabetes promotes gastrointestinal tumorigenesis in Apc-deficient mice and provides evidence of a mechanistic link between obesity and colorectal neoplasia.