On September 1, 2005, with only 12 hours notice, various collaborators established a medical facility--the Katrina Clinic--at the Astrodome/Reliant Center Complex in Houston. By the time the facility closed roughly two weeks later, the Katrina Clinic medical staff had seen over 11,000 of the estimated 27,000 Hurricane Katrina evacuees who sought shelter in the Complex. Herein, we describe the scope of this medical response, citing our major challenges, successes, and recommendations for conducting similar efforts in the future.