Prior to conducting a large-scale RCT, it is necessary to pilot test the efficacy of early cortisol treatment at reducing or preventing PTSD symptoms in a representative sample of heterogeneous trauma victims. The proposed research is designed to examine the efficacy of hydrocortisone (commercially-available cortisol) in preventing post-traumatic stress in a small-scale, randomized, double-blind trial. More specifically, incidence of PTSD and comorbid disorders (i.e., mood, anxiety and substance abuse/dependence disorders), severity of symptoms, health-related quality of life, and hormonal correlates of distress will be prospectively examined in trauma victims who are randomly assigned to receive either a course of hydrocortisone or placebo within 12 hours of the traumatic event. As psychological and physiological reactions to trauma may develop over a number of months post-trauma, prospective follow-up will allow us to examine the efficacy of cortisol administration at reducing both early as well as delayed development of symptoms. The proposed research will provide pilot data and effect size estimates for a subsequent large-scale trial, should pilot results be promising.