For the first two years of its existence, the Mayor's WTC Medical Working Group (MWG) reviewed the large body of scientific literature about the health impacts of the 2001 terrorist attacks that had accumulated to date. After summarizing the major findings in two comprehensive annual reports (see page 3) and sharing them with legislators in city and federal government, as well as other stakeholders, the MWG began addressing specific areas of interest at each of its meetings. At its September 2009 meeting, the MWG invited nearly a dozen stakeholders, including representatives of the National Institute for Occupational Safety and Health (NIOSH), academia, labor and community, and the New York City Department of Health and Mental Hygiene shared an early draft of the WTC Health Registry's 2010-2011survey. This survey, the third that the Registry will conduct, is especially critical as it will continue to examine the health of up to 70,000 people exposed to the WTC disaster nearly a decade later, not just those who have sought treatment for 9/11-related illness. MWG meeting participants offered many valuable suggestions, including increasing emphasis on development of chronic conditions such as heart disease and cancer; adding more questions about depression, which often develops in people who have post-traumatic stress disorder (PTSD); and continued probing about how enrollees access and utilize health care. In its December 2009 meeting, the MWG focused on long-term 9/11-related mental illness sequelae. In addition to the WTC Centers of Excellence, several providers with experience in service delivery participated in the meeting along with a representative from NIOSH. Together, these providers have treated thousands of New Yorkers for PTSD related to the 2001 terrorist attacks. Access to care, the current capacity for treating what appears to be a high burden of 9/11-related PTSD and mental health comorbidities, and the use of evidence-based practices in treating 9/11-related mental illness were among the topics discussed. At the April 2010 meeting, representatives from the three WTC Centers of Excellence and the WTC Health Registry each made presentations about the complex methodological questions associated with preliminary cancer investigations among their overlapping study cohorts. The Fire Department of New York (FDNY) and the WTC Health Registry, which have both begun determining the number of confirmed cancer diagnoses through 2006 within their cohorts, agreed they would co-chair a conference of outside experts, including biostatisticians and cancer epidemiologists, to help address these analytic questions and to provide invited researchers tracking each of the WTC cohorts with shared guidance for their continued analyses using the best methods available. As a result of this two-day conference, which took place in June 2010, the WTC Medical Working Group endorsed several recommendations (see page 12) that have been accepted by the WTC Centers of Excellence and the WTC Health Registry about the methods that they should use in their cancer investigations going forward. The topic of the August 2010 meeting was mortality among people who were exposed to the WTC disaster, which is closely tracked by the New York State Department of Health and the WTC Health Registry. This discussion, which took place after this report went to press, will be summarized in the 2011 MWG annual report. The WTC Medical Working Group has reviewed nearly 250 studies published from 2001 to 2010 that are relevant to its mission. The majority of these studies examined the short-term health effects of people exposed to the WTC disaster 1-4 years later. Nine years after the attack on 9/11, an increasing number of studies have progressed to the stage where mid-term health effects are now being described and analyzed. These studies indicate that while the majority of people exposed to the WTC disaster are healthy and symptom-free, thousands of individuals - including rescue, recovery and clean-up workers and people who lived, worked or went to school in Lower Manhattan on 9/11- have developed chronic, and often co-occurring, mental and physical health conditions. New research examining firefighters and emergency medical service workers and published in the New England Journal of Medicine this year (see summary beginning on page 5) demonstrates that lung damage in this group has persisted for at least 6 years.1,2 This longitudinal research, however, did not assess the impact of treatment, which may have helped to restore lung function or prevent further deterioration among many of the 13,000 individuals who were studied. Another FDNY study suggests that airway obstruction, not interstitial lung disease, is the predominant lung injury among WTC-exposed rescue workers.3 In general, health findings remain remarkably consistent across WTC studies and are summarized here.