This paper reviews evidence concerning the major risk factors for posttraumatic stress disorder. Although there are a number of consistent risk factors, their effects tend to be small and to vary according to the nature of the study. This suggests that they are not well suited to identifying individuals who require early intervention following a traumatic event. In contrast, methods based on symptom reports offer a much more sensitive and practicable approach to screening. A recent instrument, the Trauma Screening Questionnaire, is brief, simple to administer, and highly efficient at identifying survivors in need of intervention.