A good deal of research in recent years has revisited the relationship between immigration and violent crime. Various scholars have suggested that, contrary to the claims of the classic Chicago School, large immigrant populations might be associated with lower rather than higher rates of criminal violence. A limitation of the research in this area is that it has been based largely on cross-sectional analyses for a restricted range of geographic areas. Using time-series techniques and annual data for metropolitan areas over the 1994–2004 period, we assess the impact of changes in immigration on changes in violent crime rates. The findings of multivariate analyses indicate that violent crime rates tended to decrease as metropolitan areas experienced gains in their concentration of immigrants. This inverse relationship is especially robust for the offense of robbery. Overall, our results support the hypothesis that the broad reductions in violent crime during recent years are partially attributable to increases in immigration.