Background: At the end of life, formal care costs are high. Informal care (IC) costs, and their effects on outcomes, are not known. This study aimed to determine the IC costs for older adults in the last 3 months of life, and their relationships with outcomes, adjusting for care quality. Methods: Mortality follow-back postal survey. Setting: Palliative care services in England (London), Ireland (Dublin) and the USA (New York, San Francisco).