Background: Systematic screening is a powerful means by which children and adolescents with posttraumatic stress symptoms (PTSS) can be detected. Reliable and valid measures based on current diagnostic criteria are needed. Aim: To investigate the internal consistency and construct validity of the Child and Adolescent Trauma Screen (CATS) in three samples of trauma-exposed children in the US (self-reports: n = 249; caregiver reports: n = 267; pre-school n = 190), in Germany (self-reports: n = 117; caregiver reports: n = 95) and in Norway (self-reports: n = 109; caregiver reports: n = 62). Method: Internal consistency was calculated using Cronbach’s alpha. Convergent-discriminant validity was investigated using bivariate correlation coefficients with measures of depression, anxiety and externalizing symptoms. CFA was used to investigate the DSM-5 factor structure. Results: In all three language samples the 20 item symptom score of the self-report and the caregiver report proved good to excellent reliability with alpha ranging between .88 and .94. The convergent-discriminant validity pattern showed medium to strong correlations with measures of depression (r = .62-.82) and anxiety (r = .40-.77) and low to medium correlations with externalizing symptoms (r = -.15-.43) within informants in all language versions. Using CFA the underlying DSM-5 factor structure with four symptom clusters (re-experiencing, avoidance, negative alterations in mood and cognitions, hyperarousal) was supported (n = 475 for self-report; n = 424 for caregiver reports). Limitations: The external validation of the CATS with a DSM-5 based semi-structured clinical interview and corresponding determination of cut-points is pending. Conclusion: The CATS has satisfactory psychometric properties. Clinicians may consider the CATS as a screening tool and for symptom monitoring.