Objectives: The objective of this study was to assess the relationship between internet addiction and health behaviors & mental health among Korean adolescents. Methods: Data from the 2010 Korean Youth Risk Behavior Web-based Survey was analyzed. Using the Korean Internet Addiction Proneness Scale for Youth-Short Form: Self Report developed by the Korean National Information Society Agency in 2008, subjects were classified into 3 groups for internet addiction including general user, potential-risk group, and high-risk group. The health behaviors and mental health were compared among the groups for internet addiction by gender. Results: There was significantly higher prevalence of internet addiction including potential-risk group and high-risk group in boys(14.1%) than in girls(8.8%). There were significant odds ratios of perceived stress, perceived depression, perceived health and happiness, and satisfaction of sleeping in both genders at potential-risk group and high-risk group compared to general user for the internet addiction. The odds ratios of smoking at high risk group, alcohol drinking at potential risk group, eating breakfast at high risk group, and moderate physical activity at both risk groups among boys were significant. Among girls at both risk group, the odds ratios of smoking, alcohol drinking, and eating breakfast were significant. Conclusions: This study reveals a significant association among internet addiction, and health behaviors, and mental health in Korean adolescents.