Objectives: The purpose of this study was to examine the twelve-year incidence of hypertension, and to find risk factors for the incidence in adult population in Kangwha County, Korea. Methods: In 1986, 413 males(mean age 37 years) and 434 females(mean age 33 years) were examined in the Kangwha Study, Among 764 non-hypertensive participants, 164 males and 214 females were reexamined in 1998. Blood pressure(BP) was measured with standard mercury sphygmomanometers. Multiple logistic regression analysis was used to estimate the relative risk of risk factors on the incidence of hypertension. Results: During the 12-year period, 68 of 164 males and 53 of 2f4 females developed hypertension. In a multiple logistic model adjusted for age and pulse rate, baseline BP, baseline body mass index(BMI) and BMI change during the follow-up period were significantly related to the incidence of hyperiension. Adjusted relative risk(RR)s of baseline high-normal BP were 3.90(95% CI: 1.81-7.84) in males, and 12.72(95% CI: 3.70-30.73) in females. Compared with lower baseline BMI group, adjusted RRs of middle baseline BMI group were 2.66(95% CI: 1.19-5.70) in males, and 2.33(95% CI: 0.95-5.55) in females. Adjusted RRs of upper baseline BMI group were 3.52(95% CI: 1.53-7.67) in males and 3.63(95% CI: 1.50-8.43) in females. Increase of BMI was positively related to the incidence in males(adjusted RR=2.71, 95% CI: 1.00-6.71) and females(adjusted RR=3.05, 95% CI: 1.29-6.88). Conclusions: The twelve-year incidence of hypertension was 41.5% in males, and 25.8% in females. Baseline BP, baseline BMI, and BMI change were strongly related to the incidence of hypertension.