The studies reviewed show that traditional youth gangs are distinct from more highly organized adult criminal gangs or networks that exist to market narcotics. It does not appear that the street groups extensively involved in criminal activities emerged from traditional youth gangs that existed before the crack cocaine epidemic in Hispanic and African-American communities. Youth gang homicide studies uniformly suggest that violent gang activities and narcotics trafficking should be viewed as separate, important risk factors for homicide rather than as interrelated co-factors. Thus, it cannot be said that youth gangs were the main instrument in the spread of the crack cocaine epidemic. Gang-member migration for drug trafficking purposes has largely been limited to a short radius from the gangs' home turf. Nor has gang involvement in drug trafficking contributed significantly to the increase in gang homicides, except in isolated cases; rather, gang homicides are primarily endemic to everyday gang life.