Several recent clinical trials show that blocking agents of the renin-angiotensin-aldosterone system (RAAS) reduce cardiovascular events in patients with metabolic syndrome based on insulin resistance and obesity, especially accumulated visceral fat. Our laboratory has focused on the relationship between the vascular RAAS and the action of insulin on the vasculature. We first revealed that the addition of insulin to cultured vascular smooth muscle cells (VSMC) markedly increases angiotensinogen and angiotensin II (Ang II) expression and production. Insulin addition also induces VSMC growth that is inhibited by the blockade of the RAAS by either ACEI or ARB which suggests a role for the RAAS in insulin-mediated growth. Insulin has a quite different effect on cultured vascular endothelial cells (EC) as it reduces angiotensinogen and renin expression. However, insulin added to EC induces a marked activation of ACE and the activated ACE promotes the conversion of Ang I to Ang II and cell growth under conditions of high insulin concentration. Ang II induces the progression of atherosclerosis through the production of oxidative stress that blocks insulin signaling and accelerates atherosclerosis. In this paper, we attempt to clarify the relationship between insulin resistance, the RAAS, and oxidative stress in vascular tissues to mimic in vivo conditions found in patients with metabolic syndrome and obesity-related hypertension.