ABSTRACT: The purpose of the current study was to evaluate possible overlapping substance abuse and internet addiction in a large, uniformly sampled population, ranging in age from 13 to 18 years. Participants (N=73,238) in the current study were drawn from the 6th Korea Youth Risk Behavior Web-based Survey (KYRBWS-V) for students from 400 middle schools and 400 high schools in 16 cities within South Korea. Of adolescent internet users, 85.2% were general users (GU), 11.9% were users with potential risk for internet addiction (PR), and 3.0% were users with high risk for internet addiction (HR). There was a difference in the number of students with alcohol drinking among the GU, PR, and HR groups (20.8% vs 23.1% vs 27.4%). There was a difference in the number of students who smoked among the GS, PR, and HR groups (11.7% vs 13.5% vs 20.4%). There was a difference in the number of students with drug use among the GU, PR, and HR groups (1.7% vs 2.0% vs 6.5%). After adjusting for sex, age, stress, depressed mood, and suicidal ideation, smoking may predict a high risk for internet addiction (OR=1.203, p=0.004). In addition, drug use may predict a high risk for internet addiction (OR=2.591, p<0.001). Because students with a high risk for internet addiction have vulnerability for addictive behaviors, co-morbid substance abuse should be evaluated and, if found, treated in adolescents with internet addiction.