Objective To study the impact of prehypertension on carotid atherosclerotic plaque formation in a mid-dle-aged and elderly population. Methods We studied nine hundred and forty-two residents in a community of Guang-zhou,China by questionnaires,physical examinations,blood chemistry tests and bilateral carotid ultrasonography.Differ-ences of plaque formation were compared among the three populations of normotension(NT),prehypertension(Pre-HT)and hypertension(HT),which were stratified by the JNC-7 classification of blood pressure.Results Pre-HT and HT were associated with the risk factors such as older age,male gender,dyslipidemia,obesity and smoking.Adjusting for relevant risk factors,carotid atherosclerotic plaque formation rate in the Pre-HT was as 2.37 times as that of NT(95%CI:1.42～3.95,P<0.01),difference of plaque formation rate between Pre-HT and HT was not significant(P>0.05).Echolucent plaques were more prevalent in Pre-HT population than in HT population.Conclusions Prehypertension is associated with high risk of carotid atherosclerotic plaque formation and carotid atherosclerotic plaque formation are common among patients with the prehypertension in a middle-aged and elderly population.