BACKGROUND: Family caregivers play an important role in the care of patients receiving palliative care, yet little is known about the financial impact of family caregiving in this context. A lack of existing validated tools for collecting data on the costs of family caregiving in palliative care has resulted in a weak and limited evidence base. The aim of the study was to describe the development and initial piloting of a new survey tool which captures data on the costs of family caregiving in palliative care: the Costs of Family Caregiving (COFAC) questionnaire. METHODS: Development and piloting of the COFAC questionnaire involved 2 phases: (1) questionnaire development based on published evidence and cognitive interviews with service users; and (2) validity testing involving expert review and piloting with bereaved caregivers. RESULTS: Questionnaire content was generated from previously published research and related to work-related costs, carer time costs and out-of-pocket expenses. 2 group cognitive interviews with 15 service users refined content of the draft questionnaire. Face validity was established through expert review with 9 academics and clinicians. Piloting with 8 bereaved caregivers established acceptability and feasibility of administration. CONCLUSIONS: The COFAC tool has been shown to be valid, acceptable to bereaved caregivers and feasible to administer. The COFAC questionnaire is recommended for economic research in palliative care which seeks to capture data from a broad societal perspective which includes family caregiver costs.