BackgroundThere have been changes to the criteria for diagnosing post-traumaticstress disorder (PTSD) in DSM-5 and changes are proposed for ICD-11.AimsTo investigate the impact of the changes to diagnostic criteria for PTSDin DSM-5 and the proposed changes in ICD-11 using a large multisitetrauma-exposed sample and structured clinical interviews.MethodRandomly selected injury patients admitted to four hospitals wereassessed 72 months post trauma (n = 510). Structuredclinical interviews for PTSD and major depressive episode, as well asself-report measures of disability and quality of life wereadministered.ResultsCurrent prevalence of PTSD under DSM-5 scoring was not significantlydifferent from DSM-IV (6.7% v. 5.9%, z= 0.53, P = 0.59). However, the ICD-11 prevalence wassignificantly lower than ICD-10 (3.3% v. 9.0%,z =–3.8, P<0.001). The PTSDcurrent prevalence was significantly higher for DSM-5 than ICD-11 (6.7%v. 3.3%, z = 2.5, P= 0.01). Using ICD-11 tended to show lower rates of comorbidity withdepression and a slightly lower association with disability.ConclusionsThe diagnostic systems performed in different ways in terms of currentprevalence rates and levels of comorbidity with depression, but on otherbroad key indicators they were relatively similar. There was overlapbetween those with PTSD diagnosed by ICD-11 and DSM-5 but a substantialportion met one but not the other set of criteria. This represents achallenge for research because the phenotype that is studied may bemarkedly different according to the diagnostic system used.