Unsupervised peer contact in the after-school hours was examined as a risk factor in the development of externalizing problems in a longitudinal sample of early adolescents. Parental monitoring, neighborhood safety, and adolescents' preexisting behavioral problems were considered as possible moderators of the risk relation. Interviews with mothers provided information on monitoring, neighborhood safety, and demographics. Early adolescent (ages 12-13 years) after-school time use was assessed via a telephone interview in grade 6 (N = 438); amount of time spent with peers when no adult was present was tabulated. Teacher ratings of externalizing behavior problems were collected in grades 6 and 7. Unsupervised peer contact, lack of neighborhood safety, and low monitoring incrementally predicted grade 7 externalizing problems, after controlling for family background factors and grade 6 problems. The greatest risk was for those unsupervised adolescents living in low-monitoring homes and comparatively unsafe neighborhoods. The significant relation between unsupervised peer contact and problem behavior in grade 7 held only for those adolescents who already were high in problem behavior in grade 6. These findings point to the need to consider individual, family, and neighborhood factors in evaluating risks associated with young adolescents' after-school care experiences.