OBJECTIVES: A majority of South Korean adolescents experience chronic sleep-deprivation due to social jet lag. In this study, we investigated gender differences in the relationship between social jet lag, depression, and obesity in Korean children and adolescents. METHODS: Our sample consisted of 4,380 adolescents (elementary school cohort n=2,141, middle school cohort n=2,239) who participated in the Korean Children and Youth Panel Survey. In order to analyze the gender differences in the relationship between sleep time difference, obesity and depression, t-test and chi-square test were utilized. RESULTS: Both cohorts revealed that the difference in weekday/weekend sleep duration (2.19+/-1.42 vs. 1.68+/-1.36, p<0.001) and depression levels (20.77+/-6.29 vs. 18.87+/-6.06, p<0.001) was significantly higher in girls than boys. However, body mass index was higher in boys than girls (20.86+/-3.42 vs. 20.04+/-2.51, p<0.001). Chi-square test revealed there was a significant difference between gender and weekday/weekend sleep discrepancy group (cutoff >2 hours). Both elementary school [chi2 (1)=8.73, p<0.05] and middle school cohorts [chi2 (1)=61.29, p<0.001] showed significant gender differences. CONCLUSIONS: There were especially more girls who reported a discrepancy of 2 or more hours of weekday/weekend sleep duration. In summary, intervention for social jet lag may be important to consider in adolescents.