After the September 11, 2001, attacks on the World Trade Center (WTC), a comprehensive screening program was established to evaluate the physical and mental health of rescue and recovery workers and volunteers. Persons were eligible for this program if they participated in the WTC rescue or recovery efforts and met specific time criteria for exposure to the site. During July 16, 2002--August 6, 2004, the program evaluated 11,768 workers and volunteers. This report summarizes data analyzed from a subset of 1,138 of the 11,768 participants evaluated at the Mount Sinai School of Medicine during July 16--December 31, 2002. On the basis of one or more standardized screening questionnaires, approximately half (51%) of participants met threshold criteria for a clinical mental health evaluation. Continued surveillance is needed to assess the long-term psychological impact of the aftermath of the 9/11 attacks and to determine needs for continued treatment. The program was approved by an institutional review board, and informed consent was obtained for data aggregation and analyses. Participants were asked to complete standardized, self-administered questionnaires that screened for symptoms of anticipated postdisaster mental health conditions. The questionnaires used were the General Health Questionnaire-28 (GHQ), which identifies general psychiatric symptoms (1); Post Traumatic Stress Disorder (PTSD) Symptom Checklist (PCL), which identifies possible cases of PTSD (2); Patient Health Questionnaire (PHQ), which identifies panic, generalized anxiety, and depression (3); CAGE Questionnaire, which identifies likely alcohol dependence and abuse (4); and Sheehan Disability Scale, which measures functioning at home and work (5). Participants who met threshold criteria or acknowledged suicidal ideation or substantial disability on any questionnaire were referred for clinical evaluations by mental health professionals on the same day.