The 11th version of the International Classification of Diseases (ICD-11) introduces Posttraumatic Stress Disorder (PTSD) and complex PTSD (CPTSD) as two distinct trauma-related disorders. The International Trauma Questionnaire (ITQ) is the most widely used measure of assessment and has been adapted for use in children and adolescents (ITQ-CA), but a corresponding caregiver version is still missing. We aimed to close this gap by adapting the ITQ-CA and provide an initial validation of the ITQ - Caregiver Version (ITQ-CG). A corresponding measure of assessment from caregiver-perspective is integral for the use in child psychology, psychiatry and research. Altogether, 326 children and adolescents who attended the department of child and adolescent psychiatry were rated by their caregivers using a set of standardized measures. Excluding patients due to missing data or no trauma exposure, a final sample of 223 patients was analysed. Factorial structure of the ITQ-CG and multiple forms of validity were examined using confirmatory factor, latent class and correlation analysis. Confirmatory factor analysis supported the two-factor higher-order model of ICD-11 CPTSD as the factorial structure of the ITQ-CG. Convergent-divergent validity of main- and subscales of the ITQ-CG was evidenced by respective correlations with criterion variables. Latent class analysis supported the discriminant validity of the ITQ-CG, identifying a CPTSD-, PTSD-, DSO- and low symptoms-class. The CPTSD-class was associated with highest rates of comorbid psychopathology and functional impairment. Concurrent validity was evidenced by satisfactory concordance between caregiver- and child-reports. This study provides the construction and initial validation of the ITQ-CG to assess ICD-11 PTSD and CPTSD in children and adolescents from caregiver-perspective. We found compelling evidence for the ITQ-CGs validity, identifying it as an easy-to-use screening instrument to assess ICD-11 PTSD and CPTSD from caregiver-perspective. The ITQ-CG is freely available for clinicians and researchers.