The terrorist attacks of September 11, 2001 exposed rescue and recovery workers to unprecedented levels of risk for job-related injury, illness, and death. The National Institute for Occupational Safety and Health (NIOSH), a part of the U.S. Centers for Disease Control and Prevention (CDC), responded swiftly to address workers' needs in the aftermath of the attacks. NIOSH quickly sent to Ground Zero dozens of staff who applied their technical expertise to help meet immediate worker protection needs. Also, by helping workers and supervisors build their own safety and health capacity, NIOSH was able to enhance safety at the sprawling site. In the aftermath, NIOSH is working with its partners to address concerns about potential long-term effects on workers' health and to help protect workers in the event of future emergencies.