The 11th edition of the International Classification of Diseases (ICD-11; World Health Organization, 2017) proposes a model of posttraumatic stress disorder (PTSD) that includes 6 symptoms. This study assessed the ability of a classification-independent measure of posttraumatic stress symptoms, the Impact of Event Scale-Revised (Weiss & Marmar, 1996), to capture the ICD-11 model of PTSD. The current study also provided the first assessment of the predictive validity of ICD-11 PTSD. Former East German political prisoners were assessed in 1994 (N = 144) and in 2008-2009 (N = 88) on numerous psychological variables using self-report measures. Of the participants, 48.2% and 36.8% met probable diagnosis for ICD-11 PTSD at the first and second assessments, respectively. Confirmatory factor analysis supported the factorial validity of the 3-factor ICD-11 model of PTSD, as represented by items selected from the Impact of Event Scale-Revised. Hierarchical multiple regression analysis demonstrated that, controlling for sex, the symptom clusters of ICD-11 PTSD (reexperiencing, avoidance, and sense of threat) significantly contributed to the explanation of depression (R2 = .17), quality of life (R2 = .21), internalized anger (R2 = .10), externalized anger (R2 = .12), hatred of perpetrators (R2 = .15), dysfunctional disclosure (R2 = .27), and social acknowledgment as a victim (R2 = .12) across the 15-year study period. Current findings add support for the factorial and predictive validity of ICD-11 PTSD within a unique cohort of political prisoners.