Unaccompanied asylum-seeking children (UASC) are considered at high risk for mental health problems, yet few studies focus on single ethnic populations. This study presents results from the largest Afghan UASC mental health survey in the U.K. Specifically, the study aims to estimate the prevalence of emotional and behavioural problems and to investigate the associations of these problems with demographic variables, cumulative traumatic events, and care and migration variables. A census sample of 222 Afghan UASC was interviewed using validated self-report screening measures. Emotional and behavioural problems were screened using the Hopkins Symptoms Checklist 37A (HSCL-37A). Pre-migration stressful life events were screened using the Stressful Life Events Questionnaire. Administrative data on care and asylum were provided by the local authority social services and the UK Border Agency. Approximately one-third (31.4 scored above cut-offs for emotional and behavioural problems, 34.6% for anxiety and 23.4% for depression. Ordinary least squares regression indicated a significant dose-response relationship between total pre-migration traumatic events and distress as well as between increased time in the country and greater behavioural problems. Compound traumatic events in the pre-migration stages of forced migration have a deleterious association with UASC well-being. Increased time in country suggests a possible peer effect for these children. Consistent with other studies on refugee children, it should be stressed that the majority of UASC scored below suggested cut-offs, thus displaying a marked resilience despite the experience of adverse events.