Unaccompanied immigrant children continue to arrive at the US-Mexico border and are at high risk for ongoing abuse, neglect, and poor mental and physical health. We are medical and legal experts in the fields of immigrant and refugee health, child abuse, and the legal rights of international refugee and migrant children. We provide an overview of US federal agencies with custody of unaccompanied immigrant children, a summary of medical care provided while in custody, and recent findings from the independent Juvenile Care Monitor Report mandating new custodial conditions for immigrant children while in federal custody. We provide recommendations to improve the health and well-being of unaccompanied immigrant children while in custody and once released to US sponsors. (Am J Public Health. 2024;114(3):340-346. https://doi.org/10.2105/AJPH.2023.307570).