To date, health effects of exposure to the September 11, 2001 disaster in New York City have been studied in specific groups, but no studies have estimated its impact across the different exposed populations. This report provides an overview of the World Trade Center Health Registry (WTCHR) enrollees, their exposures, and their respiratory and mental health outcomes 2-3 years post-9/11. Results are extrapolated to the estimated universe of people eligible to enroll in the WTCHR to determine magnitude of impact. Building occupants, persons on the street or in transit in lower Manhattan on 9/11, local residents, rescue and recovery workers/volunteers, and area school children and staff were interviewed and enrolled in the WTCHR between September 2003 and November 2004. A total of 71,437 people enrolled in the WTCHR, for 17.4% coverage of the estimated eligible exposed population (nearly 410,000); 30% were recruited from lists, and 70% were self-identified. Many reported being in the dust cloud from the collapsing WTC Towers (51%), witnessing traumatic events (70%), or sustaining an injury (13%). After 9/11, 67% of adult enrollees reported new or worsening respiratory symptoms, 3% reported newly diagnosed asthma, 16% screened positive for probable posttraumatic stress disorder (PTSD), and 8% for serious psychological distress (SPD). Newly diagnosed asthma was most common among rescue and recovery workers who worked on the debris pile (4.1%). PTSD was higher among those who reported Hispanic ethnicity (30%), household income < $25,000 (31%), or being injured (35%). Using previously published estimates of the total number of exposed people per WTCHR eligibility criteria, we estimate between 3,800 and 12,600 adults experienced newly diagnosed asthma and 34,600-70,200 adults experienced PTSD following the attacks, suggesting extensive adverse health impacts beyond the immediate deaths and injuries from the acute event.