The combination of sarcopenia and obesity, an age-related change in body composition, is a concern in the aged society. Sarcopenic obesity is not the combination of two conditions, but is more related to cardio-metabolic and functional abnormalities. Sarcopenic obesity is associated with more physical functional decline than simple obesity. Sarcopenic obesity may be more insulin resistant, and have a higher risk for metabolic syndrome and atherosclerosis than simple obesity. However, the prevalence of sarcopenic obesity differs substantially among studies because of the lack of a standard definition. For further understanding of the pathophysiological role of sarcopenic obesity, a standardized definition for both sarcopenia and obesity is necessary.