Objective: Recently, the American Psychiatric Association (DSM-5) and the World Health Organization (ICD-11) have both revised their formulation of posttraumatic stress disorder (PTSD). The primary aim of this study was to compare DSM-5 and ICD-11 PTSD prevalence and comorbidity rates, as well as the level of disability associated with each diagnosis. Method: This study was based on a representative sample of adult Ukrainian internally displaced persons (IDPs: N = 2,203). PTSD prevalence was assessed using the PTSD Checklist for DSM-5 and the International Trauma Questionnaire (ICD-11). Anxiety and depression were measured using the Generalized Anxiety Disorder Scale and the Patient Health QuestionnaireDepression. Disability was measured using the WHO Disability Assessment Schedule 2.0. Results: The prevalence of DSM-5 PTSD (27.4%) was significantly higher than ICD11 PTSD (21.0%), and PTSD rates for females were significantly higher using both criteria. ICD-11 PTSD was associated with significantly higher levels of disability and comorbidity. Conclusion: The ICD-11 diagnosis of PTSD appears to be particularly well suited to identifying those with clinically relevant levels of disability.