With the inclusion of trauma-related cognitions in the DSM-5 criteria for posttraumatic stress disorder (PTSD), the assessment of these cognitions has become essential. Therefore, valid tools for the assessment of these cognitions are warranted. The current study aimed at validating the Dutch version of the Child Posttraumatic Cognitions Inventory (CPTCI). We included children aged 8–19 years in our study and assessed the factor structure, reliability and validity of the CPTCI in a clinical sample ( n =184) and a school sample ( n =318). Our results supported the two-factor structure of the CPTCI and showed good internal consistency for the total scale and the two subscales. We found significant positive correlations between the CPTCI and measures of PTSD, depression, and anxiety disorder. The CPTCI correlated negatively with a measure of quality of life. Furthermore, we found significantly higher scores in the clinical sample than in the school sample. For children who received treatment, we found that a decrease in CPTCI scores was accompanied by a decrease in posttraumatic stress symptoms and comorbid problems indicating that the CPTCI is able to detect treatment effects. Overall, our results suggest that the Dutch CPTCI is a reliable and valid instrument.