Hundreds of thousands of lives in the Gulf Coast region were affected by Hurricane Katrina. The Children's Health Fund (CHF) responded rapidly to the needs of children and their families after the hurricane. CHF is a national organization that supports direct health services, education, and advocacy for medically underserved children. Although CHF's principle mission is the provision of extended primary care services for children and adolescents, the organization is capable of mobilizing rapidly in response to acute medical and public health crises. In fact, the CHF has responded to catastrophic events twice before the Gulf Coast storms of 2005. The first was the 1992 deployment of a mobile medical unit (MMU) to South Florida in the immediate aftermath of category 5 Hurricane Andrew. Then, in 2001 after the terrorist attacks on the World Trade Center in New York City, New York, the CHF deployed 2 MMUs (fully equipped, self-contained “medical offices on wheels”) to the triage-and-response efforts at ground zero. Thus, in the aftermath of Hurricane Katrina, within days of the storm's landfall, the CHF was able to deploy MMUs to the Biloxi-Gulfport community in Mississippi and a number of shelter sites for displaced persons in Louisiana. The CHF developed Operation Assist and began preparations to mobilize medical teams. Developed in response to Hurricane Katrina, Operation Assist is a joint emergency-response initiative of the CHF with the National Center for Disaster Preparedness at the Columbia University Mailman School of Public Health (New York, NY). CHF's staff determined necessary staffing, supplies, housing, and safety precautions. Clearance was obtained from the Department of Health in Mississippi and Louisiana for its clinicians not only to provide health care through MMUs but also to access gasoline (in short supply at the time), medical supplies, and pharmaceuticals. In addition, the MMUs were authorized to travel … Address correspondence to Arturo Brito, MD, MPH, FAAP, The Children’s Health Fund, 215 W 125th St, New York, NY 10027. E-mail: abrito{at}chfund.org