The terrorist attacks of September 11, 2001 tragically demonstrate that civilian exposure to traumatic events has reached significant and unprecedented proportions in American society. Prior to 9/11/01, rates of post-traumatic stress disorder (PTSD) had reached nine percent in the general population and twice that in populations with repetitive exposure to critical incidents, such as emergency rescue workers (e.g. firefighters). The recent terrorist attacks and the continued threat of attacks against Americans at home underscore a pressing need to examine prevention models in addition to treatment models to avert the growing incidence of this disabling psychiatric disorder and its precursor- acute stress disorder. Acute stress disorder (ASD) is a new DSM-IV diagnostic disorder targeted to identify individuals who suffer from serious stress reactions that may develop into PTSD in the first four weeks following a trauma or disaster. Consequently, effective treatments for ASD may provide an important avenue for secondary prevention of PTSD. In fact, cognitive behavioral treatment of individuals with ASD has resulted in significant reductions in the later development of PTSD. Although this CBT represents the clinical state of the art in individual post trauma psychological interventions, no empirical studies exist that have evaluated their efficacy for group treatment. Group treatment following trauma or disasters involving many individuals, such as airline, terrorist or natural disasters, will be the most efficient public health intervention to treat acute stress reactions in survivors, and prevent the chronic and debilitating disorder of PTSD. In the proposed project, two standardized group treatment manuals for ASD will be developed: a cognitive behavioral treatment and a psychoeducational treatment. Feasibility and outcome of the two treatment manuals will be systematically tested in a group of 80 Boston metropolitan firefighters who exhibit ASD symptoms following exposure to a critical on-duty incident. Participants who exhibit acute stress symptoms will be randomly assigned 72-96 hours post event to one of the two group treatment conditions. Outcome evaluation will include psychological, physical health and work performance indices. Psychometric evaluations will be conducted at baseline preceding the critical incident, pretreatment, post-treatment and at one and three months following treatment completion. Long-term research objectives for an NIMH R01 submission include a large-scale group treatment outcome study for PTSD prevention following trauma exposure and a prospective study of pre- and post-trauma factors related to ASD and PTSD in a population of firefighter recruits.