OBJECTIVES: Increasing use of antipsychotic medications in children, especially outside of FDA approved uses has become a topic of national concern. Higher utilization of antipsychotic medications in foster children has raised questions about treatment disparities. This study assesses the relative risk of antipsychotic use in foster children compared to non-foster children in Mississippi Medicaid. METHODS: We employed a retrospective observational design. Mississippi DOM pharmacy claims for all children from ages 4-18 years and continuously enrolled for 2015 were analyzed for antipsychotic use. Antipsychotic use was identified by using NDC codes for all first and second-generation antipsychotics. Foster children were identified using eligibility codes, which excluded children who received long-term care or had dual eligibility. Poisson regression with log link was used to assess the unadjusted and adjusted relative risks of antipsychotic use amongst foster versus non-foster care children. RESULTS:  We identified 4,626 foster children and 274,043 non-foster children continuously enrolled in 2015. Foster children had higher rates of mental disorders such as psychosis, ADHD, conduct disorder, and disruptive behavior disorder. The unadjusted relative risk of antipsychotic use in foster children was 3.6 times higher compared to non-foster children (95% CI, 3.303-4.013, p<0.0001). When adjusting for demographics and mental health disorders, the relative risk of antipsychotic use dropped to 1.4 (95% CI, 1.272-1.603, p<0.0001). CONCLUSIONS: The use of antipsychotic medications was significantly higher among foster children. After adjusting for mental health and developmental conditions, the relative risk of use was still significantly higher but much lower. The drop in adjusted relative risk indicates that higher rates of use in foster children might be explained by higher rates of trauma and mental health disorders. Future work examining additional confounding variables may be needed to determine whether a treatment disparity actually exists between foster and non-foster children.