Background: In England and Wales, the Strengths & Difficulties Questionnaire (SDQ) is used to assess and monitor looked after children’s (LAC) mental health; and some targeted CAMHS teams use it to decide who can access services. However, the ability of the single-informant SDQ to identify LAC who need mental health treatment is insufficiently understood. Methods: 144 LAC referrals to a Targeted CAMHS Team were screened as part of a larger study. To establish how well the SDQ identified children who required treatment, Total Difficulties Scores (TDS) from single-informant SDQs submitted at referral were compared to treatment recommendations following routine CAMHS assessment in a real-world setting. To explain the results, clinicians (n=9) from the team were interviewed and key themes identified using Thematic Analysis. Results: Optimal accuracy calculations for SDQs completed by carers (TDS=17, sensitivity .67, specificity .57), teachers (TDS=17, sensitivity .79, specificity .71) and young people (TDS=14, sensitivity.79, specificity .42) compared to the outcome of routine CAMHS assessments indicated that the number of children whose treatment needs were not identified by their SDQ score may be unacceptably high. Key themes from clinician interviews identified possible gaps and limitations: Developmental Trauma and Attachment Difficulties, A different kind of ‘patient?’, Seeing the bad but neglecting the sad, and The importance of clinical judgement. Conclusions: Contrary to UK Government policy, this study suggests that the single-report SDQ should not be relied upon as a sole means of identifying mental health difficulties in this vulnerable, high-risk population.