Children in foster care experience higher levels and rates of psychosocial difficulties than children from the general population. Governments and child welfare services have a responsibility to identify those children in care who have need for therapeutic services. This can be achieved through systematic screening and monitoring of psychosocial difficulties among all children in foster care. However, general screening and assessment measures such as the Strengths and Difficulties Questionnaire (SDQ) and Child Behavior Checklist (CBCL) might not adequately screen for the range of difficulties experienced by foster children. The Brief Assessment Checklists for Children (BAC-C) and Brief Assessment Checklists for Adolescents (BAC-A) are measures designed to screen for and monitor attachment- and trauma-related difficulties among child welfare populations. This article reports psychometric properties of the BAC-C and BAC-A, estimated in a population study of 219 Dutch foster children. The results suggest the BAC-C and BAC-A perform both screening and monitoring functions well. Their screening accuracy, internal reliability and concurrent validity are comparable to those estimated for the SDQ within the same child and adolescent sample. Future research is needed to assess the value of the Brief Assessment Checklists (BAC) compared to other measures and to validate cut-points for the BAC. This study further establishes the BAC-A and BAC-C as valid and useful mental health screening and monitoring measures for use with children and adolescents in foster care.