This paper aims to investigate the level of posttraumatic stress and depressive symptoms, and background risk and protective factors that might increase or ameliorate this distress amongst unaccompanied asylum-seeking children and adolescents (UASC). Cross-sectional survey carried out in London. Participants were 78 UASC aged 13–18 years, predominantly from the Balkans and Africa, compared with 35 accompanied refugee children. Measures included self-report questionnaires of war trauma, posttraumatic stress and depressive symptoms. UASC had experienced high levels of losses and war trauma, and posttraumatic stress symptoms. Predictors of high posttraumatic symptoms included low-support living arrangements, female gender and trauma events, and increasing age only amongst the UASC. High depressive scores were associated with female gender, and region of origin amongst the UASC. Conclusion: UASC might have less psychological distress if offered high-support living arrangements and general support as they approach the age of 18 years, but prospective studies are required to investigate the range of risk and protective factors.