We examined the immediate, short- and long-term effectiveness of the SNAP[TM] Under 12 Outreach Project (ORP)--a community-based program for children under the age of 12 at risk of having police contact. Sixteen pairs of children were matched on age, sex and severity of delinquency at admission, and randomly assigned to the ORP or to a control group which received less intensive treatment. Level of antisocial behavior was assessed pre and post intervention (immediate effects) and at three follow-up periods (up to 15 months post treatment) to investigate maintenance of possible treatment effects. A search of criminal records was also performed to assess long term effects. Results indicated that ORP children decreased significantly more than controls on the Delinquency and Aggression subscales of the Child Behavior Checklist pre- to post-intervention, and these effects were maintained over time. For statistically significant differences, effect sizes were large (0.79 to 1.19). Fewer ORP children (31%) had criminal records at follow-up compared to controls (57%), although this difference was not statistically significant. Overall, the ORP appears to be an effective cognitive-behavioral program for antisocial children in the short term, with possible effects that extend into adolescence and adulthood.