Recent studies into the underlying factor structure of posttraumatic stress symptoms often report factor structures that do not replicate the three symptom cluster of re-experiencing, avoidance and arousal symptoms as classified within the Diagnostic and Statistical Manual of Mental disorders (American Psychiatric Association, 1994, 2000). Data from 485 emergency service personnel who had experienced an occupational trauma were submitted to confirmatory factor analysis to test seven alternative factor models of posttraumatic stress symptoms. This study is one of the most comprehensive structural analyses of posttrauma symptoms to date. The model of best fit comprised four first-order factors including intrusion, avoidance, numbing and arousal alongside a general PTSD factor. This study highlighted the difference between the current DSM symptom groupings and those derived empirically. (c) 2006 Elsevier Ltd. All rights reserved.