Background: Until now, the relations between the working alliance and trauma-related symptoms have received little or no study in residential-care settings. However, considering the high prevalence of past experiences of interpersonal trauma among young people in residential centers, it is essential to examine this issue more closely. Objective: This study aimed to determine to what extent the strength of the working alliance, as reported by adolescent girls in residential centers and their counselors, is associated with the trauma-related symptoms that these girls reported subsequently, in emerging adulthood. Methods: The sample consisted of 130 adolescent girls placed in residential center. Trauma-related symptoms were measured at intake and approximately 4 years later, when all the girls were out of the center. Working alliance was measured 3 months after the start of the placement. Hierarchical multiple regressions were performed to determine the strength of the relationships between the working alliance during treatment and trauma-related symptoms in emerging adulthood. Results: Findings showed that even after controlling for intake symptoms, the strength of the working alliance reported by the girls has modest, yet significant, negative associations with several trauma-related symptoms in emerging adulthood. The stronger the alliance the girls reported, the less they reported symptoms of depression, post-traumatic stress and externalization. Conclusions: Results suggest that a strong working alliance with adolescent girls may contribute to their recovery as it was associated with less trauma-related symptoms. Further research is needed to investigate the mechanisms and underlying factors explaining this relationship at short, medium and long term.