text: The World Trade Center Health Registry was established in 2002 by ATSDR and the New York City Department of Health and Mental Hygiene to track the long-term physical and mental health effects of the September 11 attacks. The registry contains more than 71,000 people who lived, worked, or went to school near the World Trade Center site, as well as emergency response personnel who were involved in rescue and recovery efforts. It is the largest post-disaster health registry in the United States. Researchers use the registry to study the health effects of the disaster and to develop public health recommendations for future disasters. A 2009 study based on registry data found that posttraumatic stress disorder and asthma were the two most commonly reported conditions among registry participants 5 to 6 years after the disaster. The study found that 19% of adult participants reported new posttraumatic stress symptoms, and 10% of adult participants reported developing new asthma.