To establish the best approach to develop a quality of life (QoL) questionnaire for cancer-patient caregivers, this study attempts to identify primary domains of QoL in terms of their impact on a purposive sample of caregivers. Seventy-seven informal adult caregivers of cancer patients (breast cancer, paediatric haematological malignancies or melanoma) with different relationships with the patients (parents, children, spouses, siblings, and friends) were recruited at three specialised French centres and extensively interviewed.