This study identified risk factors for suicide ideation among adolescents through a secondary analysis using data collected over five years from the 5th–9th Korea Youth Risk Behavior Survey. We analyzed 370,568 students' responses to questions about suicidality. The risk factors for suicide ideation included demographic characteristics, such as gender (girls), low grades, low economic status, and not living with one or both parents. Behavioral and mental health risk factors affecting suicide ideation were depression, low sleep satisfaction, high stress, alcohol consumption, smoking, and sexual activity. Health care providers should particularly target adolescents manifesting the above risk factors when developing suicide prevention programs for them.