Objective: This systematic review and meta-analysis examined cross-informant agreement concerning mental health outcomes for maltreated children. This study provides important information to individuals working with maltreated children (e.g., clinicians, child welfare practitioners) who must make critical decisions related to safety, mental health, and permanency. Method: We retrieved 29 studies that collected mental health data for maltreated children using standardized instruments. We were able to examine 4 informant pairs and 7 mental health outcomes. Results: Agreement across children’s mental health outcomes was highest for child–caregiver pairs (small to large, significant effect sizes), followed by child–teacher and caregiver–teacher (small to medium, significant effect sizes) and then caregiver–caregiver (small, nonsignificant effect sizes) pairs. Agreement generally was highest for overt behaviors. Conclusions: It is important to include children as informants, gather teacher and caregiver data when assessing child internalizing difficulties, and examine specific maltreatment outcomes (e.g., traumatic stress). Clinically, it is critical to understand why different informants perceive a child’s functioning in different ways for purposes of prognosis and treatment planning for the child and his or her family. It is also critical to triangulate data sources when assessing for maltreatment impact and to consider data points that both converge and diverge when making appropriate safety and treatment plans.