Young people who grow up in care and then exit care around the age of 18 (care-leavers) are a particularly vulnerable group, at increased risk for mental health problems even relative to other care-experienced groups. Yet, little is understood about the factors underpinning this association. We used scoping review methods to synthesize the quantitative and qualitative literature on factors that are associated with mental health problems for care-leavers. Following rigorous methods, we systematically searched three scientific databases spanning psychology and social care and identified 23 peer-reviewed studies for inclusion. This review highlights the heterogeneity of this research, in terms of methodology and topics investigated. Topics included are as follows: pre-care maltreatment, care-related experiences, psychological factors (emotion regulation), social support, education, and adult functioning (e.g., housing, finances, employment). We found mixed and inconsistent findings across research studies. The strongest evidence-base is around the influence of social support upon the mental health of recent care-leavers, though methodological problems are discussed. The field benefits from several large-scale observational and longitudinal research studies. However, there is an over-reliance upon retrospective reporting, and the use of unvalidated measures is common. It is apparent that there are significant gaps in our current understanding of the mental health of care-leavers, in particular around modifiable factors. We discuss potential directions for future empirical research, both in terms of methodology and factors investigated.