Posttraumatic stress disorder (PTSD) is a significant problem among Iraq/Afghanistan-era veterans. To date, however, there has been only limited research on how the recent changes in DSM-5 influence the prevalence and factor structure of PTSD. To address this key issue, the present research used a modified version of a gold-standard clinical interview to assess PTSD among a large sample of Iraq/Afghanistan-era veterans (N = 414). Thirty-seven percent of the sample met DSM-5 criteria for PTSD compared to a rate of 38% when DSM-IV diagnostic criteria were used. Differences in rates of diagnosis between DSM-IV and DSM-5 were primarily attributable to changes to Criterion A and the separation of the "avoidance" and "numbing" symptoms into separate clusters. Confirmatory factor analysis (CFA) was used to compare the fit of the previous 3-factor DSM-IV model of PTSD to the 4-factor model specified in DSM-5, a 4-factor "dysphoria" model, and a 5-factor model. CFA demonstrated that the 5-factor model (re-experiencing, active avoidance, emotional numbing, dysphoric arousal, anxious arousal) provided the best overall fit to the data, although substantial support was also found for the 4-factor DSM-5 model. Low factor loadings were noted for two of the symptoms in the DSM-5 model (psychogenic amnesia and reckless/self-destructive behavior), raising questions regarding the adequacy of fit between these symptoms and the other core features of PTSD. Overall, findings suggest the DSM-5 model of PTSD is an improvement over the previous DSM-IV model of PTSD, but still may not represent the true underlying factor structure of PTSD.