Purpose: This study aims to validate the Dutch-Flemish PROMIS pediatric item banks v2.0 Anxiety and Depressive Symptoms, the short forms 8a, and computerized adaptive tests (CATs) in a general Dutch population and to provide reference data. Methods: Participants (N = 2,893, aged 8–18), recruited by two internet survey providers, completed both item banks. These item banks were assessed on unidimensionality, local independence, monotonicity, Graded Response Model (GRM) item fit, and differential item functioning (DIF) for gender, age group, region, ethnicity, and language. The short forms and CATs were assessed on reliability and construct validity compared to the Revised Child Anxiety and Depression Scale short version (RCADS-22) subscales. Reference scores were calculated. Results: Both item banks showed sufficient unidimensionality, local independence, monotonicity, and GRM item fit, except for three Depressive Symptoms items that showed insufficient GRM item fit. No DIF was found when using ordinal regression analyses, except for two Depressive Symptoms items that showed DIF for language; all items showed DIF for language when using IRT PRO, except for one Anxiety item. Both short forms and CATs revealed sufficient reliability for moderate and severe levels of anxiety and depression, as well as high positive correlations with corresponding RCADS-22 subscales and slightly lower correlations with non-corresponding RCADS-22 subscales. Conclusion: The Dutch-Flemish PROMIS pediatric item banks v2.0 Anxiety and Depressive Symptoms, the short forms 8a and CATs are useful to assess and monitor anxiety and depression in a general population. Reference data are presented.