Violence is a leading cause of injury, death, and mental health problems for America's youth. Although physicians and other health care professionals have always been involved in treating the results of violence, recent research and practice suggest that we can also play a critical role in its prevention. We have two opportunities for intervention and prevention: during a routine health care visit and when caring for a youth who has been injured. On these occasions we can provide preventive education, screening for risk, and linkages to intervention and follow-up services. This guide was written to: provide basic information about youth violence, describe risk factors and appropriate screening tools, suggest approaches to violence prevention and intervention present ideas and resources for advocacy and research. This guide does not focus on determining who is a victim and who is a perpetrator, as these distinctions are often blurred when dealing with youth violence. Instead, this guide will focus on identifying known risk factors and predictors for violent behavior, in order to reduce injury for all youths at risk. Each patient contact is an opportunity for us to listen, counsel, and teach. As health care professionals, we can make a significant impact in the prevention of youth violence.