In a 10-year prospective study, we investigated the utility of the serum creatinine level in predicting the development of hypertension in Japanese adults, all of whom lived in a rural community. The study included 229 subjects, 91 men and 138 women aged 30 to 69 years, who were normotensive (systolic blood pressure 140 mm Hg or less and diastolic blood pressure 90 mm Hg or less) and had no prior history of antihypertensive treatment at baseline (1979 to 1980). Hypertension was defined as systolic blood pressure more than 140 mm Hg and diastolic blood pressure more than 90 mm Hg and starting antihypertensive medication. Stepwise proportional hazard analysis selected serum creatinine (P < .001) as an independent, significant predictor of hypertension together with systolic blood pressure (P < .001), age at entry (P < .001), body mass index (P = .008), and diastolic blood pressure (P = .011). The age- and sex-adjusted relative risk for subjects with a serum creatinine level of 1.2 mg/dL or higher compared with those with a level less than 1.1 mg/dL was 0.42 (95% confidence interval, 0.25 to 0.71). The mechanism of this association might relate to muscle mass and physical exercise or, possibly, to a primary renal abnormality. It appeared that the serum creatinine level may be useful in predicting future hypertension.