Aims: The aims of this study are to describe informal care activities and to estimate the societal cost of informal care of community-dwelling frail elderly people in Sweden. Methods: This study was performed within the frame of the TREEE project that included 408 frail elderly patients. At index hospitalisation (baseline), primary informal caregivers of the patients were provided with a questionnaire on informal care during a period of three months. Questions concerning other (secondary) informal caregivers were also included.