The terrorist attacks of September 11, 2001, were quickly followed by predictions of an epidemic of new cases of posttraumatic stress disorder (PTSD) and major depression. It was unclear how many people had received enough traumatic exposure to increase their risk of these disorders. Had a New Yorker who saw the planes hitting the twin towers on television "experienced, witnessed, or confronted" a traumatic event, as described in DSM-IV? But estimates of the number of new cases, extrapolated from the Oklahoma City bombing and other disasters, surpassed 100,000. Subsequent news reports indicated a surge in mental health visits and in the consumption of junk food, cigarettes, and alcohol.

Nonetheless, it is unclear whether greater use of mental health services reflects new psychiatric cases or the reactivated, elevated needs of previously diagnosed patients. New York clinicians did see patients who had DSM-IV acute stress disorder—a "normal" response to catastrophe?—that typically resolved after a visit or two. Most patients I have seen, ranging from those who ducked falling bodies and debris to those who were miles from Ground Zero, presented with exacerbations of preexisting mood, anxiety, psychotic, and substance use disorders. Research indicating that patients who have extant psychiatric vulnerabilities are the most vulnerable to trauma is consistent with this anecdotal observation.

Epidemiological studies will define the psychiatric aftershocks of September 11. But if a new patient cohort does not materialize, why not? I believe that the wonderfully supportive response to the tragedy may have cushioned its effects. Nothing so terrible had ever hit New York City before September 11, but neither had anything so good as what followed. The outpouring of public support in the city, across the country, and around the world was something to behold. New Yorkers, not previously known for their civic warmth, warmed up. Support services sprang into existence. This generosity, solidarity, and resurgence in morale may have tempered the sequelae of an enormous trauma. We are assessing this supportive effect in a PTSD study.

Another positive result of the tragedy is the New York City Consortium for Trauma Treatment, organized by psychiatric departments of major New York hospitals and funded by the charity 9/11. The consortium is teaching local clinicians evidence-based treatments for trauma-based psychiatric disorders. Beyond meeting the needs of traumatized patients, this organization has the potential to reeducate clinicians across New York City, bringing them up to date with the best validated treatments for anxiety, mood, and other disorders.