Aim: This study aims to assess the quality of life and quality of care as experienced by patients with advanced cancer and their relatives while taking their interdependency into account. Methods: A prospective multicentre observational study (eQuiPe study) was conducted. Quality of life scores (EORTC QLQ-C30) was compared to a matched normative population and logistic regression analyses were conducted to assess the relation between high emotional functioning (EF, measured with the EORTC QLQ-C30) and experienced quality of care (IN-PATSAT32, CQ-index PC). Results: In total, 1103 (65%) patients and 831 (71%) relatives completed the baseline questionnaire, including 699 unique patient-relative couples. Patients experienced lower EF than the normative population (78 versus 87, p <.001). Compared to patients, relatives reported clinically relevantly lower EF (69 versus 78, p <.001). Being more satisfied with care in general (p <.05) and clarity about the key health-care provider (p <.05) was positively associated with high EF in patients. For relatives, experienced continuity of care (p <.01) and information for the patient (p <.05) were positively associated with high EF. The EF of patients (p <.001) and relatives (p <.001) were positively associated with each other and continuity of care as perceived by relatives was positively associated with high EF in patients (p <.01). Conclusions: Patients with advanced cancer reported low levels of EF but their relatives reported even lower levels of EF. Experienced integrated organisation and satisfaction with care were positively related to EF. The interdependent relation between patients' and relatives’ EF and their care experiences suggests that a family-centred approach can optimise palliative cancer care. Trial registration: The eQuiPe study is registered as NTR6584 in the Netherlands Trial Register.