The purpose of this study was to determine the differences in internet use motivations and problem behaviors among vocational high school students according to internet addiction and family system type. Five hundred vocational high school students from Daegu took part in the survey. The questionnaire survey consisted of an internet addiction self-assessment scale, a family system type scale, an internet use motivation scale, and a problem behavior scale. The data was analysed using MANOVA and Cronbach a, and the $Scheff\acute{e}$ test was used for post-hoc analysis. The major findings of this study were as follows: First, the study found significant differences in adolescent internet use motivation according to internet addiction. Adolescents in the high dangerous user group showed higher communicative, experiential, and addictive motivations than adolescents in potentially dangerous and normal user groups. Also, there were no significant differences in informative motivation according to internet addiction. Regardless of internet addiction, adolescents tend to use the internet to search for information and to solve problems. Second, there were significant differences in adolescents' problem behaviors according to internet addiction. More specifically, adolescents who were in the high dangerous user group displayed more problem behaviors toward their body, family, school, and society than adolescents in the potentially dangerous and the normal user groups. Third, an adolescent's family system type significantly influenced his/her internet use motivation. Adolescents from an extreme family showed higher communicative and addictive motivations than adolescents from middle and balanced families. Fourth, there were significant differences in the problem behaviors of adolescents according to family system types. Adolescents from an extreme family showed more problem behaviors toward their body, family, school, and society than adolescents from middle and balanced families.