On September 11, 2001, a jet aircraft crashed into the north tower of the World Trade Center (WTC) in lower Manhattan. Minutes later, a second aircraft crashed into the south tower. The impact, fires, and subsequent collapse of the buildings resulted in the deaths of thousands of persons. The precise number and causes of deaths could not be assessed in the immediate aftermath of the attack; however, data were available on the frequency and type of injuries among survivors (Figure 1). In previous disasters, such information assisted in characterizing type and severity of injuries and the health-care services needed by survivors. To assess injuries and use of health-care services by survivors, the New York City Department of Health (NYCDOH) conducted a field investigation to review emergency department (ED) and inpatient medical records at the four hospitals closest to the crash site and a fifth hospital that served as a burn referral center. This report summarizes findings of that assessment, which indicated that the arrival of injured persons to this sample of hospitals began within minutes of the attack and peaked 2 to 3 hours later. Among 790 injured survivors treated within 48 hours, approximately 50% received care within 7 hours of the attack, most for inhalation or ocular injuries; 18% were hospitalized. Comprehensive surveillance of disaster-related health effects is an integral part of effective disaster planning and response.