The framework defined specific mechanisms and processes by which neighborhood disadvantage includes adolescent outcomes. The research used path analysis to test the hypothesis that these organizational and cultural features of neighborhoods mediate the effects of ecological disadvantage of adolescent development and behavior. Hierarchical linear modeling (HLM) was then used to estimate the unique contribution of neighborhood effects on youth outcomes with respect to prosocial competence, conventional friends, and problem behavior such as juvenile delinquency or drug use. The sample included households with at least one youth aged 10, 12, 14, 16, or 18 years. Data were collected by means of interviews with all eligible youths and the mother or primary caregiver in each household. The participants included 662 families and 820 youths in 33 block groups. Results supported the study hypothesis. Findings also indicated that the unique influence of neighborhood effects is relatively small. However, these effects account for a substantial part of the variance explained by the HLM model in most cases. Figures, tables, notes, and 54 references (Author abstract modified)