There is a very close interrelationship between the metabolic disorders such as obesity and diabetes mellitus and cardiovascular diseases such as hypertension and atherosclerosis, with insulin resistance and endothelial dysfunction as common features. Insulin has vasculoprotective effects through production of nitric oxide in the endothelial cells, while it produces atherogenic effects by stimulating proliferation and migration of vascular smooth muscle cells(VSMC). The insulin-activated pathway is the phosphatidylinositol 3-kinase pathway in the endothelial cells and MAP kinase pathway in the VSMC. Insulin resistance and hyperinsulinemia may result in the attenuation of the endothelium-mediated action and stimulation of the VSMC-mediated action. Insulin resistance and endothelial dysfunction are related to each other and may cause vicious cycle, leading to the metabolic and cardiovascular diseases.