Hypertension has long been recognized as a major risk factor of several cardiovascular diseases. It is well known that the renin-angiotensin system(RAS) is involved in the pathogenesis of both hypertension and hypertensive end-organ damage. Untreated hypertension is self-accelerating condition through RAS stimulation. Activation of RAS contributes to the transition from borderline hypertension to established hypertension. Recently, "the Seventh Report of Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC 7)" proposed a new classification of borderline blood pressure levels, as "prehypertension". The therapeutic focus has begun to shift from the therapy of established hypertension to the prevention of hypertension. This review addressed the relationship between hypertension, prehypertension and the role of RAS.