Objectives: This study was conducted to estimate medical expenditure attributable to overweight and obesity in adults with hypertension, diabetes and dyslipidemia using Korea National Health and Nutrition Examination survey data and Korea National Health Corporation data. Methods: The medical expenditure of hypertension, diabetes and dyslipidemia related to overweight and obesity were composed of inpatient care costs, outpatient care costs and medication costs. The population attributable risk (PAR) of overweight and obesity was calculated from national representative data of Korea such as the National Health Insurance Corporation cohort data and 2005 Korea National Health and Nutrition Examination survey data. Results: The medical expenditure attributable to overweight and obesity of hypertension were 456 billion won (men : 215 billion won, women : 241 billion won). Those of diabetes were 282 billion won (men : 148 billion won, women : 135 billion won), and of dyslipidemia were 17 billion won (men : 9 billion won, women : 8 billion won). Consequently, these costs corresponded to 33.3% of total medical expenditure due to hypertension, diabetes and dyslipidemia. Conclusions: We found a substantial medical expenditure due to overweight and obesity of hypertension, diabetes and dyslipidemia were very high. In order to reduce these costs, effective national strategies for prevention and management of overweight and obesity should be established and implemented.