Purpose: The purpose of this study was to explore the factors that influence risk-taking behavior in middle school students. Methods: The participants in this study were 544 students from 4 middle schools in Seoul or Gyeonggi Province. From July 16, to September 9, 2008, data were collected using self-report questionnaires. Demographic, individual, socio-economic characteristics of risk-taking behavior were examined. Descriptive statistics, t-test, ANOVA, Pearson correlation coefficients, zero-inflated negative binomial regression as count model using SAS 9.1 and Stata 10.0 program were used for the analysis. Results: The score for risk-taking behavior of the middle school students tended to be low with thrill-seeking behavior being the highest. Risk-taking behavior was higher for boys and for students not living with parents. Stress coping ability, family risk factors, family functioning, peer`s risk-taking behavior, and harmful environment were correlated with risk-taking behavior. On zero-inflated negative binomial regression analysis, the factor significantly influencing risk-taking behavior were self-esteem and for increased risk-taking behavior, family functioning, and peer`s risk-taking behavior. Conclusion: A risk-taking behavior approach that considers developmental needs is useful in understanding the behavior of early adolescents. Development of effective guidance and interventions considering factors influencing risk-taking behavior as identified in this study is recommended.