Young people living in out-of-home care often have a history of adverse childhood experiences which are traumatic in nature and have long-term influence on individuals. This article analyses the experiences of Finnish young adults with a history of out-of-home care and mental health challenges, in regard to their experienced trauma and interpretations of the traumatizing factors during their early lifespan. The ecological systems theory by Bronfenbrenner is used as a tool in the analysis. The article sheds light on how the experiences of trauma are connected to the levels of the ecological systems theory and how different social factors can contribute to the experience of trauma. Understanding the traumatic experiences of adolescents with an OOHC background requires a thorough consideration of all the levels of the ecological systems theory. Traumatization is often a fusion of acute, chronic and complex traumas that should be better acknowledged in child welfare work.