It is well established that genetic factors play an important role in the development of type 2 diabetes mellitus (DM2) and its chronic complications, and that genetically susceptible subjects can develop the disease after being exposed to environmental risk factors. Therefore, great efforts have been made to identify genes associated with DM2. Uncoupling protein 2 (UCP2) is expressed in several tissues, and acts in the protection against oxidative stress; in the negative regulation of insulin secretion by beta cells, and in fatty acid metabolism. All these mechanisms are associated with DM2 pathogenesis and its chronic complications. Therefore, UCP2 is a candidate gene for the development of these disorders. Indeed, several studies have reported that three common polymorphisms in UCP2 gene are possibly associated with DM2 and/or obesity. Only a few studies investigated these polymorphisms in relation to chronic complications of diabetes, with inconclusive results.