This article reports on the influence of neighborhood-level deprivation and collective efficacy on children's antisocial behavior between the ages of 5 and 10 years. Latent growth curve modeling was applied to characterize the developmental course of antisocial behavior among children in the E-Risk Longitudinal Twin Study, an epidemiological cohort of 2,232 children. Children in deprived versus affluent neighborhoods had higher levels of antisocial behavior at school entry (24.1 vs. 20.5, p less than 0.001) and a slower rate of decline from involvement in antisocial behavior between the ages of 5 and 10 (-0.54 vs. -0.78, p less than 0.01). Neighborhood collective efficacy was negatively associated with levels of antisocial behavior at school entry (r = -0.10, p less than 0.01) but only in deprived neighborhoods; this relationship held after controlling for neighborhood problems and family-level factors. Collective efficacy did not predict the rate of change in antisocial behavior between the ages of 5 and 10. Findings suggest that neighborhood collective efficacy may have a protective effect on children living in deprived contexts. (Contains 3 footnotes, 4 tables, and 3 figures.)