OBJECTIVES: Validated questionnaires help the preventive child healthcare (PCH) system to identify psychosocial problems. This study assesses the psychometric properties and added value of the Strengths and Difficulties Questionnaire (SDQ) for the identification of psychosocial problems among preschool-aged children by PCH. METHODS: We included 839 children (response 66%) 3 to 4 years of age undergoing routine health assessments in 18 PCH services across the Netherlands. Child healthcare professionals interviewed and examined children and parents. Before the interview, parents completed the SDQ and the Child Behavior Checklist (CBCL). We assessed the internal consistency, the scale structure, and validity (correlation coefficients, sensitivity, and specificity), with CBCL and treatment status as criteria, and the degree to which the SDQ could improve identification solely on the basis of clinical assessment. RESULTS: The internal consistency of the SDQ total difficulties score was good (Cronbach's a, 0.78), but it was worse for some subscales of the SDQ (range, 0.50-0.74). The area under the receiver operating characteristic curve using the CBCL as a criterion was 0.94 (95% confidence interval 0.91-0.97), and sensitivity and specificity were 0.79 and 0.93, respectively. The SDQ added information to the clinical assessment; the odds ratio was 36.48 for added information by using the CBCL as a criterion. CONCLUSIONS: The SDQ is a valid tool for the identification of psychosocial problems in preschool-aged children by PCH. However, the low reliability of some SDQ subscales does not justify use of these subscales for decisions about further treatment. Copyright © 2013 by the American Academy of Pediatrics.