PURPOSE: This study aimed at exploring relationships among Internet addiction, smoking, and drinking and examining the effect factors on Internet addiction, smoking and drinking. METHODS: By using stratified sampling, 1,529 participants representing high school students in the Kangwon province were selected. Data was analyzed by SPSS 12.0. using chi-square, Pearson correlation coefficient and multiple regression. RESULTS: One-fifth of the total participants were at the mild or moderate stage of Internet addiction. Regarding smoking, 22.7% of male subjects and 4.5% of female subjects were current smokers. Regarding drinking, the percentages of subjects who drank alcohol once or twice per month were 53.5% of male students and 40.7% of female students. Internet addiction positively correlated with depression, novelty seeking, harm avoidance and reward dependence, Internet addiction negatively correlated with persistence, self-directness, cooperativeness, and self-transcendence. Significant factors affecting Internet addiction were depression, gender, novelty seeking, and self-transcendence. Important factors influencing smoking were drinking, gender, school type, satisfaction with school, novelty seeking, and reward dependence. Significant factors affecting drinking were smoking, novelty seeking, school type and ages. CONCLUSION: This study shows the necessity of developing and implementing effective intervention programs in order to prevent adolescents from experiencing Internet addiction and health risk behaviors.