Objectives：As internet users increase rapidly, internet addiction is a rising addictive behavior associated with psychiatric problems of adolescence in Korea. The objectives of this study were to investigate the prevalences of internet use and the relations of internet addiction to emotional and behavioral problems of adolecence in Korea. Methods：We assessed 1.555 middle and high school students in Koyang city, Korea using Young Internet Addiction Scale (YIAS), Center for Epidemiological Study for Depression (CES-D), Revised Children’s Manifest Anxiety Scale (RCMAS), Youth Self Report (YSR), and Psychological Self (PS)-1 of Offer’s Self Image Questionnaire (OSIQ). Results：Ninty eight subjects (6.3%) were Internet Addicted Group (‘Addicted Group’)：51 (6.2%) were middle school students, and 47 (6.5%) were high school students. Compared to girls, boys showed higher prevalences of internet addiction and higher mean score of YIAS. But there were no significant differences of prevalences and YIAS scores between middle and high school students. Addicted Group had significantly higher mean scores of all scales (subscales) than Non-Addicted Group. Conclusion：Adolescents with internet addiction showed more psychiatric problems compared to adolescents without internet addiction, thus require therapeutic approaches to multiple psychopathologies in addition to the addictive behaviors.