Mental health facilities should be equipped to care for patients while preventing spread of COVID-19. Peer-reviewed literature and guidelines for government and health organizations were reviewed to guide best practices. Gunderson's five therapeutic functions of a milieu are used as a conceptual framework. Patients should be screened for infection according to local or national policy prior to admission to an inpatient mental health unit. While interacting with one another in a therapeutic milieu, patients should be encouraged to practice physical distancing and hand hygiene. Clinicians may need to alter therapeutic groups to prevent COVID-19 infection. Additionally, clinicians should monitor patients for emerging symptoms and conduct rapid testing and isolation of patients suspected of COVID-19. Recommendations are made for patients unable to adhere to physical distancing or hand hygiene policies.