Type 2 diabetes mellitus (DM2) is characterized by excessive hepatic gluconeogenesis, increased insulin resistance and a progressive inability of pancreatic beta cells to produce sufficient insulin. DM2 evolves as a progression from normal glucose tolerance, to impaired glucose tolerance (IGT) to frank diabetes mellitus, reflecting the establishment of insulin resistance and beta cell dysfunction. Insulin resistance not only contributes to impaired glycemic control in DM2, but to the development of hypertension, dyslipidemia and endothelial dysfunction. Cardiovascular disease is the primary morbidity for patients with DM2. The onset of insulin resistance and cardiovascular insult likely occurs well before the onset of IGT is detected clinically. Biguanides and thiazolidinediones (TZDs) are two classes of oral agents for the management of DM2 that improve insulin resistance, and thus have potential cardiovascular benefits beyond glycemic control alone. Metformin additionally inhibits hepatic gluconeogenesis. The combined use of two of these agents targets key pathophysiologic defects in DM2. Single pill combinations of rosiglitazone/metformin and pioglitazone/metformin have recently been approved for use in the US and Europe. This article reviews the clinical data behind the use of metformin in combination with TZDs for the management of diabetes, its impact on vascular health, side effects and potential mechanisms of action for combined use.