In the months after the September 11, 2001, attacks on the World Trade Center (WTC), concerns grew about the health consequences of exposures sustained by persons involved in the rescue and recovery response. In addition to the estimated 10,000 Fire Department of New York (FDNY) personnel, an estimated 30,000 other workers and volunteers potentially were exposed to numerous psychological stressors, environmental toxins, and other physical hazards. These concerns prompted CDC's National Institute for Occupational Safety and Health (NIOSH) to support the WTC Worker and Volunteer Medical Screening Program, which provided free, standardized medical assessments, clinical referrals, and occupational health education for workers and volunteers exposed to hazards during the WTC rescue and recovery effort. During July 16, 2002-August 6, 2004, the program evaluated 11,768 non-FDNY workers and volunteers. This report summarizes data analyzed from a subset of 1,138 of the 11,768 participants evaluated at Mount Sinai School of Medicine during July 16-December 31, 2002. These data indicated that a substantial proportion of participants experienced new-onset or worsened preexisting lower and upper respiratory symptoms, with frequent persistence of symptoms for months after their WTC response work stopped. These findings underscore the need for comprehensive health assessment and treatment for workers and volunteers participating in rescue and recovery efforts.