Hurricane Katrina made landfall on August 29, 2005, with major impact on the U.S. Gulf Coast. During August 29-September 11, surveillance identified 22 new cases of Vibrio illness with five deaths in persons who had resided in two states. These illnesses were caused by V. vulnificus, V. parahaemolyticus, and nontoxigenic V. cholerae. These organisms are acquired from the environment and are unlikely to cause outbreaks from person-to-person transmission. No cases of toxigenic V. cholerae serogroups O1 or O139, the causative agents of cholera, were identified. This report summarizes the investigation by state and local health departments and CDC, describes three illustrative cases, and provides background information on Vibrio illnesses. Results of the investigation underscore the need for heightened clinical awareness, appropriate culturing of specimens from patients, and empiric treatment of illnesses (particularly those associated with wound infections) caused by Vibrio species. No confirmed cases of illness have been identified with onset after September 5; additional Vibrio cases are under investigation.