Introduction: Attachment disorder (AD), including reactive AD and disinhibited social engagement disorder, is a prevalent, yet underdiagnosed disorder in severely maltreated children. Because the condition is associated with significant psychiatric morbidity over the entire lifespan, a valid and economic screening tool to identify children with clinical symptoms of AD is needed to avoid unspecific or ineffective treatment. The present study aimed to assess the effectiveness and efficiency of the German version of the Relationship Problems Questionnaire (RPQ). Methods: With a total of 135 children (mean age = 7.17 years, SD = 1.40, 63% male) from both general (34 children) and high-risk populations (69 in- and outpatients, 32 foster children), we investigated the sensitivity and specificity of the RPQ. AD was diagnosed using a standardized clinical interview (K-DIPS). 35 out of 135 children fulfilled the criteria for AD. Results: The RPQ identified 74% of the children who fulfilled the criteria for AD in the standardized clinical interview. The optimal cut-off score of the RPQ for identifying AD was 4.5 with a moderate sensitivity of 0.74 and specificity of 0.68. Conclusions: The German version of the RPQ proved useful as a diagnostic indicator of clinical symptoms of AD. The tool is economic and suitable for the screening of AD in the general population as well as high-risk populations. We recommend the use of the RPQ in clinical and research settings, adding multi-method approaches after a positive screening.