The authors investigated a recent reformulation (Brewin, Lanius, Novac, Schnyder, & Galea, 2009) of posttraumatic stress disorder (PTSD) in treatment-seeking civilian trauma survivors. Diagnostic data from a randomized controlled trial (N = 170) were subjected to the criteria according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; American Psychiatric Association, 1994) and the Brewin criteria for PTSD. Results revealed no change in PTSD prevalence, though substantial but equal (13%) proportions of participants lost or gained a PTSD diagnosis under the Brewin criteria. Rates of comorbid depression and other anxiety disorders were consistently marginally lower under the Brewin criteria, but these differences did not reach significance in the authors' sample. It was concluded that the 8-item Brewin criteria for PTSD altered the diagnostic status of a substantial number of participants without influencing overall PTSD prevalence or comorbidity.