Syrian children affected by the civil war are at increased risk of mental health problems, including depression, anxiety, post-traumatic stress disorder (PTSD), and externalizing behaviour problems. Screening questionnaires are designed to identify individual children who require further assessment and treatment, and also estimate the need for mental health services in a population. However, few questionnaires have been rigorously tested in this population. This study examined the reliability and validity of questionnaires for depression (Center for Epidemiological Studies Depression Scale for Children, CES-DC, self-report, 10-item version), anxiety (Screen for Child Anxiety Related Emotional Disorders, SCARED, self-report, 18-item version), PTSD (Child PTSD Symptom Scale, CPSS, self-report), and internalizing and externalizing behavior problems (Strengths and Difficulties Questionnaire, SDQ, parent-report version) in a population sample of 8-17 year old Syrian children living in Informal Tented Settlements (ITS) in the Beqaa region of Lebanon. In addition, several ways of measuring functional impairment due to mental health problems were compared. These included self- and parent-report questionnaires (World Health Organization Disability Assessment Schedule, WHODAS-Child; SDQ Impact supplement, parent-report only) and an interviewer rating of severity (Clinical Global Impression–severity, CGI-s). Questionnaires were translated into Arabic and modified based on pilot testing with Syrian children. Responses from N=1006 children and caregivers were used for analysis, a subset of whom had additional clinical interview data (MINI KID + clinical judgement; N=119). The self-report questionnaires showed good internal consistency reliability with alpha>.80, though the parent-report SDQ and WHODAS-Child fell below this level. In terms of validity, the SDQ externalizing scale performed well in differentiating children with conduct problems from those without and it was possible to achieve a fair balance between sensitivity (82%) and specificity (71%). The CES-DC, CPSS, SDQ total difficulties, and WHODAS-Child (selfreport) achieved an acceptable level of validity, though it was harder to achieve a good balance between sensitivity and specificity. In most cases, at least 50% of those screening positive were false positives, meaning that a more in-depth follow up assessment would be required if these tools were used as screeners in a clinical setting. Furthermore, correctionwould be needed if used to estimate prevalence rates for mental disorders in this population. There was moderate convergent validity between measures of functional impairment, with self-report WHODAS-Child showing greater agreement with interviewer ratings when compared to parent-report measures (WHODAS and SDQ Impact). Measuring functional impairment and distress due to mental health problems should help to differentiate children with clinically significant mental health problems from those with subthreshold problems; however, more work will be required to establish how helpful the tools used here are in achieving that aim.