Boston, like many other major cities, experienced a sudden increase in youth homicides during the late 1980s and early 1990s. Research evidence suggests that the recent epidemic of urban youth violence was intensely concentrated among criminally active young black males residing in disadvantaged urban neighborhoods rather than all young black males residing in disadvantaged black neighborhoods. Other researchers, however, suggest that there was a diffusion of guns and gun violence from youth involved in street crack markets to youth outside the drug trade who armed themselves primarily for self-protection against the armed criminally active youth. In this paper, criminal history data are analyzed to determine whether the criminal profile of Boston arrested youth gun offenders changed over time and micro-level data on youth gun assault incidents in Boston are examined to unravel whether there were noteworthy changes in the nature of these violent events over time. The results of these analyses suggest that the youth violence epidemic in Boston was highly concentrated among serious youth gun offenders rather than a diffusion of guns away from the street drug trade, gangs, and criminally active youth.