The aim of this study was to identify the 'high-normal blood pressure' as a risk factor of hypertension for applying primary prevention strategy in Korean people. To keep time sequence of events, and to prevent information bias, nested casecontrol study was chosen for avoiding measurement errors because hypertension is a benign disease. Source population consisted of the 'Seoul Cohort' participants and follow-up was done by using Korea Medical Insurance Corporation's database on the utilization of health services from January 1, 1993 to June 30, 1997. Incidence cases were ascertained through the chart review, telephone contacts, and direct blood pressure measurements. Controls included the pairing of 4 individuals to each case on the basis of age. The statistically significant risk factors of hypertension were body mass index, dietary fiber, alcohol consumption, weekly activity, and history of quitting smoking as well as high-normal blood pressure (p<0.05). The multivariate odds ratio of high-normal blood pressure adjusted for all risk factors was 1.84 (95% CI, 1.31-2.56). Thus, the 'high-normal blood pressure' is considered as a risk factor for hypertension in Korean middle-aged men, which suggests that the vigorous lifestyle modification for persons with 'high-normal blood pressure' is needed.