Rosiglitazone and pioglitazone are medications from the thiazolidinedione class of compounds currently available for the treatment of type 2 diabetes mellitus. Traditionally used to enhance insulin sensitivity and decrease plasma insulin levels, added applications have emerged beyond those involving glycemic control. Cardiovascular risk factors associated with insulin resistance such as elevated blood pressure, dyslipidemia, abnormal fibrinolysis, and endothelial and vascular dysfunction have been shown to improve after thiazolidinedione treatment. Therapy with rosiglitazone or pioglitazone has been found to modify vascular reactivity and other processes involved in atherosclerosis. There may be differences between the agents in their effects on plasma lipid characteristics and particle size. These agents serve as excellent adjuncts to oral and insulin therapy for patients with type 2 diabetes mellitus and hold promise for the prevention of cardiovascular disease associated with the insulin resistance syndrome. Clinical trials are in progress to determine whether such therapy will lead to a reduction in cardiovascular events.