Although it has been demonstrated that the sympathetic nervous system participates in the genesis of essential hypertension, it is still unclear whether this system can also account for the increased incidence of arterial hypertension in diabetic patients. However, there are some observations which make this hypothesis extremely likely. In fact, it has been demonstrated that in diabetic normotensive patients the reflex control of the sympathetic discharge is normal, but in hypertensive patients there are some derangements of the autonomic nervous tone control which may contribute to increasing the incidence of arterial hypertension in patients with Type 2 diabetes mellitus. In particular, on the one hand, it has been reported that in hypertensive patients hyperinsulinemia is able to induce a reflex activation of the sympathetic tone which is 3-fold higher than that observed in normotensive subjects. On the other hand, it has been demonstrated that this abnormal sympathetic response is particularly harmful in subjects prone to develop essential hypertension since they are characterized by vascular insulin resistance, which plays a permissive role in the development of essential hypertension. Vascular insulin resistance is a type of endothelial dysfunction which impairs the insulin modulation of the vascular effects of sympathetic nervous activation.