In this study, we examine whether youth who are exposed to more weapons violence are subsequently more likely to behave violently with weapons. We use data collected with a 3-cohort, 4-wave, 10-year longitudinal study of 426 high-risk youth from Flint, Michigan, who were second, fourth, or ninth-graders in 2006–2007. The data were obtained from individual interviews with the youth, their parents, and their teachers, from archival school and criminal justice records, and from geo-coded criminal offense data. These data show that early exposure to weapons violence significantly correlates at modest levels with weapon carrying, weapon use or threats-to-use, arrests for weapons use, and criminally violent acts 10 years later. Multiple regression analyses, controlling for children’s initial aggressiveness, intellectual achievement, and parents’ income, education, and aggression, reveal statistically significant independent 10-year effects: (1) more early exposure to weapon use within the family predicts more using or threatening to use a gun; (2) more cumulative early violent video game playing predicts more gun using or threatening to use weapons, and normative beliefs that gun use is acceptable; (3) more cumulative early exposure to neighborhood gun violence predicts more arrests for a weapons crime; and (4) more cumulative early exposure to movie violence predicts more weapon carrying. We argue that youth who observe violence with weapons, whether in the family, among peers, or through the media or video games, are likely to be infected from exposure with a social–cognitive–emotional disease that increases their own risk of behaving violently with weapons later in life.