BMI is a proxy measure for adiposity in population-based studies and it is well established that increasing body fat is strongly associated with component features of the metabolic syndrome (MetS), such as dyslipidaemia (low high density lipoprotein cholesterol (HDL-C) and high triglyceride concentrations, increased glucose concentrations, high blood pressure, hypertension, and type 2 diabetes. Whether any or all of these components of the MetS account for relationships between body fatness and all cause mortality is uncertain, but we have recently shown in a large Korean cohort that co-existing cardiovascular disease (CVD), diabetes or hypertension explained much of the increased risk of CVD mortality in obese individuals. Recently, the concept of metabolically healthy obesity (MHO) has been used to try and help explain the ‘obesity paradox’, where there is decreased mortality in some people with obesity. Additionally, whether any association between underweight and increased all cause mortality is due to the presence of pre-existing cardiovascular and metabolic disease states (or risk factors) is not fully understood. Therefore, i will discuss whether BMI was associated with mortality outcomes after subjects with established risk factors and diseases such as diabetes, cardiovascular disease, hypertension and features of the MetS had been excluded.