In this study, we investigate the individual-, parents-, and family-related variables affecting the internet overuse of adolescents by the gender, school grades and school systems, which is based on surveys of 480 students in the middle and high school, employing multiple regression analysis. Major findings are as follows. 1. In the case of male students, internet use was higher when the students are playing online games more often, when the students are under stress, or when they have lower self control. In the case of female students, internet use was higher when the students are playing online games more often or when the students are visiting pornographic sites more often. 2. In the case of middle school students, internet use was higher when the students play online games more often, when they use file downloads more often, when they have lower self control, or when they have parents who are setting lesser rules on the students' internet use. In the case of high school students, internet use was higher when they play online games more often, when they engage in internet club activities more actively, when they have lower self control, when they use e-mails less frequently, when they have fathers with better internet ability, or when they are under parents' strict control. 3. In the case of academic high school students, internet use was higher when they play online games more often, when they engage in internet club activities more actively, when they visit pornographic sites more often, when they have lower self control, when they have mothers with poor internet ability, when they use e-mails less frequently, or when they have fewer number of close friends. In the cases of vocational high school students, internet use was higher when they play online games more often, when they are under more stress, when they get better grades, when they have fathers with better internet ability, when they are under parents' strict control, or when they have lower self control.