Objective: Family caregivers play an essential role in end-of-life care but suffer considerable impact on their own health. A better understanding of main factors related to carers' health is important to inform interventions. The purpose of the study was to test for the first time the potential impact of a comprehensive set of observable variables on carer health during end-of-life caregiving within a population-based carer sample. Design National retrospective, cross-sectional, 4-month post-bereavement postal census survey of family carers of people who died from cancer. Methods: Relatives who registered a death from cancer during a 2-week period in England were identified from death certificates by the Office of National Statistics; response rate was 1504/5271 (28.5%). Outcome measures Carers' mental health was measured through General Health Questionnaire (GHQ)-12; general health was measured through EuroQoL EQ-Visual Analogue Scale (EQ-5D VAS). Methods Survey questions to measure potential variables associated with carer health were based on past research and covered patients' symptoms and functioning; caregiving activities and hours; informal and formal help received; work hours, other caregiving, volunteering; changes to work, income and expenditure; sleep and relaxation; and demographic variables. Bivariate analyses and ordinary least square regression were performed to investigate these variables' relationship with outcomes. Results: Patients' psychological symptoms and functioning, caregiving hours, female gender and self-sought formal help related to worse mental health. General practitioner and social care input and relaxation related to better mental health. Patients' psychological symptoms, caregiving hours and female gender were associated with worse general health, and older age, employment and relaxation were associated with better general health. Conclusions: Improvements in carers' health overall may be made by focusing on potential impacts of patients' psychological symptoms on carers, facilitating respite and relaxation, and paying particular attention to factors affecting female carers.