Objectives Fostering, a professional or semi-professional role that is in increasing demand, involves potential exposure to material related to children's trauma in a domestic setting. Yet, professional vulnerability to secondary traumatic stress (STS) is under-researched in foster carers, as is the suitability of associated intervention techniques. We therefore investigated incidence of STS and psychological predictors relevant to secondary and primary stress appraisal in UK foster carers. Methods British foster carers (n = 187; 81% female; aged 23-72 years; mean length of experience 9 years) were approached through a range of organizations managing paid foster caring in the UK for a survey study. Self-report measures were obtained on STS, burnout and compassion satisfaction from the Professional Quality of Life (ProQOL) scale, as well as on primary trauma and variables previously recommended for inclusion in training targeting secondary trauma: empathy, resilience and self-care. Results High levels of STS and burnout were found among foster carers. In multivariate model testing, STS was directly and positively predicted by burnout, compassion satisfaction and primary trauma (R 2 = 0.54, p < 0.001). Resilience, empathy and self-care did not show direct associations with STS, but self-care had a significant indirect effect on STS. Conclusions Findings support the view that STS is a substantial risk factor in foster caring. While self-care is confirmed as a promising factor in intervention, the roles of empathy and resilience are more ambiguous.