As it has become clear that most individuals exposed to trauma do not develop PTSD, it has become increasingly important to examine pretrauma risk factors. However, PTSD research has overwhelmingly relied on retrospective accounts of trauma, which is beleaguered by problems of recall bias. To further our understanding of PTSD's etiology, a systematic review of 54 prospective, longitudinal studies of PTSD published between 1991 and 2013 were examined. Inclusion criteria required that all individuals were assessed both before and after an index trauma. Results revealed six categories of pretrauma predictor variables: 1) cognitive abilities; 2) coping and response styles; 3) personality factors; 4) psychopathology; 5) psychophysiological factors; and 6) social ecological factors. The results indicated that many variables, previously considered outcomes of trauma, are pretrauma risk factors. The review considered these findings in the context of the extant retrospective PTSD literature in order to identify points of overlap and discrepancy. Pretrauma predictor categories were also used to conceptualize variable risk for PTSD. Limitations and directions for future research are discussed. Copyright © 2013 Elsevier Ltd. All rights reserved.