The objective of this study was to investigate whether the relationships of appendicular muscle mass (ASM) with insulin resistance (IR) and metabolic syndrome (MS) vary by gender or obesity. Data of 10 146 normal-weight and obese men and women aged 19 to 93 years from the Korea National Health and Nutrition Examination Survey in 2009 and 2010 were analyzed. In normal-weight men and women, unadjusted odds ratio (OR) of being MS and IR significantly increased with lower ASM/wt. After adjusting for lifestyle factors, these ORs were still significant in normal-weight men but not in women. After controlling for other covariates, lower ASM/wt was related to higher risk for IR but not to MS in obese men. In obese women, relationship of lower ASM/wt with higher risk for MS disappeared after adjusting for covariates. Association between skeletal muscle mass and cardiometabolic abnormalities is dependent on gender and obesity in Korean adults.