Background: Leptin is a hormone that regulates food intake and body weight. It has been demonstrated that the plasma leptin levels correlates with body adiposity. Increased adiposity is accompanied by a low insulin sensitivity, which turns into insulin resistance. Recent studies suggest a complex interrelationship between leptin and insulin or insulin resistance. Therefore, the relationship between leptin and the variables of body adiposity, and insulin resistance in a non-diabetic population was examined. Methods: 555 healthy non-diabetic people aged 20 to 80 were enrolled in this study. Leptin was measured by the mean radioimmunoassay. Multiple logistic regression analysis was performed with leptin as a dependent variable and with age, sex, BP, the lipid profile, the fasting plasma glucose levels, HOMA-IR and the trunk fat contents as independent variables. Results: The plasma leptin concentrations were higher in women than in men. The leptin concentrations correlated with the body fat content, BMI and HOMA-IR but, less so with age, the fasting plasma glucose levels, the postprandial glucose levels, total cholesterol and LDL-cholesterol levels. After adjusting for the body mass index, the leptin levels significantly correlated with both the body fat content and the HOMA-IR. The results between males and females were similar when the data was analyzed after dividing by gender. Gender, the trunk fat content, HOMA-IR, and the total cholesterol and HDL cholesterol levels were independent variables which influences the log transformed leptin in multiple logistic regression analysis. When the subjects were grouped according to the number of insulin resistance syndrome including dyslipidemia, obesity, hypertension, and glucose intolerance, there was a linear increase in the leptin concentration with an increase in the number of the components of insulin resistance syndrome. Conclusion: The plasma leptin concentrations are related to adiposity, insulin resistance, and dyslipidemia in the non-diabetic Korean population. The relationship between leptin and insulin resistance independent of body fat suggests that insulin resistance might play some role in the development of hyperleptinemia and vice versa (J Kor Diabetes 26:100~111, 2002).