<sec> <title>Objectives</title> <p>To examine health behaviors among Korean adolescents with a focus on both individual and school-based factors, specifically in relation to predictors of high-risk groups.</p></sec> <sec> <title>Methods</title> <p>Secondary data analysis was conducted with data from the 8th Korea Youth Risk Behavior Web-Based Survey, using descriptive statistics, t tests, χ² test, and multilevel logistic regression analysis. Health Practice Index was calculated and a range of 0 to 2 was classified as a high-risk group.</p></sec> <sec> <title>Results</title> <p>The results revealed that the individual-level variables of sex, age, stress, depression, subjective health status, school performance, health education, father’s level of education, and living situation were significant predictors of high-risk behaviors. The risk was greater in girls, greater with higher age and higher stress scores, greater in adolescents with depression, greater with lower paternal educational level, and greater in adolescents who did not live with both parents, as were the school-level variables of school grade and school affluence score. The possibility of being in the high-risk group in health behavior was greater if a student attended a school where the Family Affluence Score (FAS) was lower.</p></sec> <sec> <title>Conclusion</title> <p>School health education should be expanded to manage students’ high-risk health behaviors, especially in schools that have many students from families with a low affluence status.</p></sec>