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.