The prevalence of type 2 diabetes is increasing dramatically in minority adolescents in association with the increased frequency of obesity. Nevertheless, carefully controlled studies of the use of oral hypoglycemic agents have not been performed in youth with type 2 diabetes. The efficacy of Metformin compared to placebo in adolescents with type 2 diabetes will be studied by assessing the change from baseline in fasting plasma glucose (FPG) at 16 weeks of double blind treatment. This study is being conducted in cooperation with the Yale Pediatric Pharmacology Research Unit (PPRU) and the NICHD PPRU network.