Internet addiction, especially its prevalence among adolescents and its predictors, has been the focus of much research. Few studies have investigated gender differences in the relationship between Internet addiction and psychological health among adolescents. The present study investigated gender differences in Internet addiction associated with self-rated health, subjective happiness, and depressive symptoms among Korean adolescents aged 12 to 18 years using a nationally representative dataset. Data from 56,086 students (28,712 boys and 27,374 girls) from 400 middle schools and 400 high schools were analyzed. We found that 2.8 % of the students (3.6 % boys and 1.9 % girls) were addicted users, and the prevalence of Internet addiction was higher in boys than in girls. In multiple logistic regression analysis, three psychological health indicators including poor self-rated health, subjective unhappiness, and depressive symptoms were significantly related with Internet addiction in boys and girls. Girls with emotional difficulties such as subjective unhappiness or depressive symptoms had much higher risks of Internet addiction than did boys with similar problems. Further attention should be given to developing Internet addiction prevention and intervention programs that are tailored to fit boys’ and girls’ different needs.