 This is a double-blind, placebo-controlled trial in which trauma victims are randomized to receive a single intranasal administration of either Oxytocin 40IU or placebo within the first six hours following trauma exposure. To provide a pre-treatment baseline, participants will receive a medical and psychological evaluation prior to treatment. After two weeks the research assistant or study psychiatrist will perform behavioral ratings and complete history details pertaining to PTSD risk factors. Participants will be assessed again by the study psychiatrist or research assistants at 1, 3, 6 and 13 months. Eligible subjects will include men and women over the age of 18, who have been exposed to an event meeting the DSM-IV A.1 criterion for trauma exposure, and who provide written, informed consent to participate in the study. In order to recruit persons who are more likely to be at risk for the development of PTSD, we will only randomize persons expressing marked anxiety, emotional distress or dissociation, as assessed by the Visual Analog Scales. Potential participants will be recruited from trauma victims arriving at the Chaim Sheba Medical Center Emergency Room. 