Introduction: Thyroid hormones play the roles of regulation of basal metabolism and energy homeostasis. Metabolic syndrome (MetS) is a medical disorder characterized by obesity, hyperglycemia, dyslipidemia, and hypertension. Hence, thyroid function test has been primarily conducted to evaluate the cause of obesity and MetS in children and adolescents as well as adults. This study investigated to explore the relationship between serum thyrotropin (TSH) and the risk of obesity and MetS in euthyroid children and adolescents. Materials and Methods: 1932 participants with euthyroidism (free thyroxine [FT4], 0.8 – 1.8 ng/dL; thyroid peroxidase antibody (TPO Ab) ≤34 IU/mL based on previous studies and manufacturer), aged 10-18 years, who had available data from KNHANES VI (2013-2015) were classified into 2 groups according to TSH level as high TSH (＞4.5 IU/mL, 270 subjects) and normal TSH (0.4 – 4.5 IU/mL, 1,662 subjects). The differences of anthropometric, biochemical, socioeconomic, and behavioral data between two groups were analyzed. Results: The mean of systolic blood pressure (BP), TSH, and FT4 and the proportion of obesity were greater in subjects with high TSH. After adjustment of all confounding factors including free T4 and TPO Ab levels, the body mass index (BMI) (R2 =0.111, P = 0.041), waist circumference (WC) (R2 = 0.151, P =0.015), systolic BP (R2 = 0.097, P = 0.001), and metabolic score (R2 = 0.017, P = 0.007) were positively changed with increasing TSH levels. After multivariate logistic regression analysis, the subjects with high TSH had greater risks of obesity (OR [95% CI], 3.137 [1.752-5.614]; P 0.001), abdominal obesity (2.238 [1.292-3.876]; P = 0.004), systolic BP (2.462 [1.121-5.406]; P = 0.025), and MetS (3.026 [1.228-7.458]; P = 0.016), compared with subjects with normal TSH. Conclusion: Korean children and adolescents with subclinical hypothyroidism should be assessed for presence of the obesity and metabolic syndrome, even if their FT4 is in normal range.