This study concerned the mental health of Afghan unaccompanied asylum-seeking children in the United Kingdom (UK). Afghans are the largest group of children seeking asylum in the UK, yet evidence concerning their mental health is limited. This study presents an estimate of probable posttraumatic stress disorder (PTSD) within this group and describes its associations with the cumulative effect of premigration traumatic events, immigration/asylum status, and social care living arrangements. Male adolescents (N = 222) aged 13–18 years completed validated self-report screening measures for traumatic experiences and likely PTSD. One-third (34.3%) scored above a selected cutoff, suggesting that they are likely to have PTSD. A higher incidence of premigration traumatic events was associated with greater PTSD symptomatology. Children living in semi-independent care arrangements were more likely to report increased PTSD symptoms when compared to their peers in foster care. A substantial majority in this study did not score above the cutoff, raising the possibility of notable levels of resilience. Future research should consider approaching mental health issues from a resilience perspective to further the understanding of protective mechanisms for this at-risk population.