Hurricane Katrina made landfall on August 29, 2005, on the Gulf Coast of the United States, causing loss of life, widespread property damage, and power outages. After hurricanes, some residents use portable generators and other gasoline-powered appliances for electrical power and cleanup. These devices produce carbon monoxide (CO), and improper use can cause CO poisoning. During August 29-September 24, a total of 51 cases of CO poisoning were reported by hyperbaric oxygen (HBO2) facilities in Alabama, Louisiana, and Mississippi. This report describes these cases and the rapidly implemented reporting system that identified them. CO poisoning can be prevented by reducing exposure to CO through appropriate placement and ventilation of gasoline-powered engines.