Polygenic risk scores and brain structures both contribute to externalizing behavior in childhood A study in the Adolescent Brain and Cognitive Development (ABCD) cohort

•Externalizing behavior is associated with smaller brain volumes, but not white matter integrity, and could largely be explained by total brain volume.•Polygenic risk scores (PRS) for externalizing-related phenotypes are associated with externalizing behavior in childhood.•PRS for aggressive-related externalizing behaviors are associated with global brain volumes and white matter integrity.•Total gray matter volume mediated the association between the PRS for disruptive behavior in ADHD and externalizing behavior.•PRS for aggressive-related externalizing behaviors and brain structures have a unique contribution to externalizing behavior.