Objective: To determine the effectiveness of the Friend to Friend (F2F) aggression prevention program through a clinical trial with urban African American girls. Method: A randomized parallel-group study design was conducted comparing the effectiveness of F2F to an attention control condition (called Homework, Study Skills, and Organization, HSO) among relationally aggressive girls from 6 urban low-income elementary schools. Analyses of covariance were utilized for comparing posttest measurements from the 2 conditions while adjusting for pretest measurements. To further explore program outcomes, we examined whether the significant intervention effects were maintained from posttest to follow-up among girls in the F2F group. Results: Results suggest that aggressive girls in F2F decreased their levels of relational aggression and increased their knowledge of social problem solving skills in comparison with similar girls randomized to HSO. Each of these findings was maintained at the 1-year follow-up. Conclusion: The F2F Program, a culturally adapted group intervention addressing multiple forms of aggression, appears to have promise for decreasing relational aggression and improving knowledge of problem solving skills for urban high risk aggressive girls, with results that are maintained 1 year after treatment. (PsycINFO Database Record (c) 2015 APA, all rights reserved)