The purpose of this study was to predict waist circumference (WC) on the basis of body mass index (BMI), gender, and age data and BMI on the basis of WC, gender, and age data in Korean adults. The subjects included 1,465 Korean adults aged 20-85 years old who visited a Promotion of Health Center for inclusive medical test during 2010; gender, age, BMI, and WC measurement data were taken. BMI (kg/m(2)) was calculated from height and weight. WC was measured at the part of the trunk located midway between the lower costal margin and the iliac crest while the subject was standing. As a result of predicting WC, the F-value was 1181.686 (p < 0.001) and R-2 was 70.8%. The best-fit multiple regression equation is as follows: WC (cm) = 34.302 + (-5.317 x gender) + (0.059 x age) + (1.999 x BMI). As a result of predicting BMI, the F-value was 1118.146 (p < 0.001) and R2 was 69.6%. The best-fit multiple regression equation is as follows: BMI (kg/m(2)) = -2.782 + (1.279 x gender) + (0.016 x age) + (0.310 x WC). Because the regression models of WC based on the data of BMI, gender, and age and BMI based on the data of WC, gender, and age have significant predictive value, we conclude that they can be used in clinical practice to identify metabolic syndrome.