Purpose: Suicide was considered as a big public health concern in recent years because suicide mortality has been increased rapidly. This study was to investigate the prevalence and risk factors of suicidal ideation among adolescents in South Korea. Methods: The data of 2007 Youth Health Risk Behavior Web-based Survey collected by Korean Center for Disease Control were analyzed using logistic regression for this study. Results: The prevalence of suicidal ideation was 23.7% in South Korea. The risk factors of suicide ideation were depression (odds 8.43), perceived stress(odds 4.30), drug use (odds 2.47), sexual intercourse(odds 2.36), present smoking (odds 1.76), present alcohol drink (odds 2.39), feeling unhappiness (odds 2.89), living with none of parents (odds 1.71), gender(odds 1.72), health status (odds 1.66), and socioeconomic status (odds 2.0). Conclusion : Health risk behaviors and mental health status were related to suicide ideation. Health risk behavior such as smoking and drinking prevention programs and mental health promotion programs should be implemented to decrease suicide ideation among adolescents. Suicide, mental health and health risk behaviors should be prevented through comprehensive health promotion programs.