The database covers 2,226 homicide incidents that involved 2,415 victims and 2,650 offenders over the 7-year period. Twenty-eight percent of the victims of these homicides were under 25 years old, and 35 percent of the offenders were younger than 25 years old. Generally, youth who committed homicide killed people of the same age group and racial group as themselves. Patterns of homicide among people under age 25 were found to be different from those of people over age 25. Youth who killed were more likely than older people to kill strangers. Whereas homicides by older people were likely to have resulted from a conflict in a relationship, homicide by youth stemmed primarily from altercations or occurred in the course of other crimes. Youth used firearms much less than older people. Youth involvement in homicides, whether as perpetrators or victims, was often the result of lifestyle and routine-activity patterns. Youth tend to spend more time away from home than older people, and they tend to visit places associated with an increased risk of involvement in violence. Based on this conclusion, the key to homicide prevention is to focus on the most dangerous situations and on people who are at highest risk of victimization. Increased police presence in places known to attract large numbers of youth and the use of environmental design are among the many situational measures that can be used to prevent youth homicide. Innovative strategies to manage and control people's use of alcohol should also be an integral part of any program aimed at preventing violence. 10 figures and 5 references