Comprehensive surveillance of disaster-related health effects is an integral part of effective disaster planning and response. Such information assists in characterizing type and severity of injuries and the health-care services needed by survivors. The impact of aircraft crashing into the World Trade Center, fires, and subsequent collapse of the buildings resulted in the deaths of thousands of persons. 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. 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 percent received care within 7 hours of the attack, most for inhalation or ocular injuries; 18 percent were hospitalized. Among the 1,688 ED patients who received care at the sampled hospitals during the assessment period, 1,103 were survivors treated for injuries or illness and the attack was not established for 96 patients because of incomplete documentation; specific injury or illness was missing for 161, and admission and discharge data were not documented for 108. Of 1,103 survivors, the median age was 39 years, 729 were male, 282 arrived by emergency medical vehicle, and 320 were rescue workers. A total of 810 were treated and released from EDs, 181 were hospitalized for additional treatment, and 4 died during emergency care. Among the survivors, 152 had WTC-related noninjury (cardiac, respiratory, neurologic, or psychiatric illness). The injury pattern among rescue workers differed from the pattern among other survivors. A significantly higher percentage of rescue workers sustained ocular injuries, and a significantly lower percentage of rescue workers sustained burns. 2 tables, 2 figures, 10 references