Abstract: ObjectiveTo investigate the effect of environmental risk factors on essential hypertension(EH)under the similar genetic background.MethodsThe study selected 60 sibs(one was hypertensive and the other was normotensive) for a paired case-control study.The data were analyzed with mulitple conditional logistic regression using SPSS 12.0 software.ResultsThere was no statistical difference in smoking,drinking,blood fat,blood sugar,serum potassium,serum sodium,serum calcium between hypertensive and normotensive group(P>0.05).The hypertensive individuals had higher body mass index(BMI)than the corresponding normotensive individuals.BMI was a risk factor of EH(P<0.05)with an odds ratio of 29.330(95% confidence interval:2.594-331.613)from multiple conditional logistic regression.ConclusionBMI may be a risk factor of EH under similar genetic background.