BACKGROUND@#The influence of socioeconomic status (SES) on weight status varies depending on the countries' levels of social and economic development. There are many studies on a risk of adolescent obesity according to familial SES in Korea. However, it is not clarified what effects familial SES has on a risk of underweight in Korean adolescents. This study investigated the distribution of weight status including obesity and underweight according to familial SES in Korean adolescents.@*METHODS@#This cross-sectional study involved 63,741 adolescents who participated in the 2016 Korea Youth Risk Behavior Wed-based Survey. The data on height, weight, familial SES, current smoking status, current alcohol intake, physical activity, breakfast skipping, perceived stress, depressive mood, and living with family were obtained through online questionnaires. The assessment of familial SES was based on perceived household economic status and parental education level.@*RESULTS@#In boys, low household economic status was related to a high proportion of obesity (odds ratio [OR] 1.14, 95% confidence interval [CI] 1.04–1.25) and underweight (OR 1.31, 95% CI 1.14–1.51). Girls with low household economic status were more likely to be obese (OR 1.81, 95% CI 1.61–2.03) and overweight (OR 1.41, 95% CI 1.23–1.60) but, although not statistically significant, less likely to be underweight (OR 0.88, 95% CI 0.75–1.04).@*CONCLUSIONS@#This study showed that adolescents with low familial SES were at a high risk of obesity and underweight. A risk of underweight was increased in boys with low familial SES but in girls with high familial SES.