Objective: Women have higher rates of posttraumatic stress disorder (PTSD) than men. The authors examined prior trauma, PTSD, major depression, anxiety disorder not including PTSD, and peritraumatic dissociation; current peritraumatic dissociation; and passenger injury as possible explanations for the different rates of acute PTSD in women and men after a serious motor vehicle accident. Method: Subjects age 18-65 years who had been in a serious motor vehicle accident (N = 122) were assessed with the Structured Clinical Interview for DSM-III-R and the Peritraumatic Dissociative Experiences Questionnaire - Rater Version 1 month after the accident. Results: Women did not differ from men in meeting the overall reexperiencing criterion for a diagnosis of PTSD (criterion B), but women were at greater risk for the specific reexperiencing symptoms of intense feelings of distress in situations similar to the motor vehicle accident and physical reactivity to memories of the motor vehicle accident. Women were 4.7 times more likely than men to meet the overall avoidance/numbing criterion (criterion C) and 3.8 times more likely to meet the overall arousal criterion (criterion D). Women were more likely than men to report the criterion C symptoms of avoiding thoughts and situations associated with the accident, loss of interest in significant activities, and a sense of foreshortened future and the criterion D symptoms of trouble sleeping, difficulty concentrating, and exaggerated startle response. Multiple logistic regression analysis indicated that the gender differences in acute PTSD were not associated with prior trauma, PTSD, peritraumatic dissociation, major depression, or anxiety disorder not including PTSD or with passenger injury. However, peritraumatic dissociative symptoms at the time of the accident were associated with a significantly higher risk for acute PTSD in women than in men. Conclusions: Gender differences in peritraumatic dissociation may help explain differences in risk for PTSD and for some PTSD symptoms in women and men.