Caregiver burden is an increasing problem with patients surviving longer and more care tasks falling to informal caregivers. While research has identified patient and caregiver variables associated with caregiver burden, less research has focused on aspects of the care environment. The present study investigated the available support and unmet needs of 57 patients with advanced cancer, 45 of their carers and 40 of their health professionals. Carers and patients consistently identified higher levels of available support for the patient than health care professionals, with carers identifying higher levels of support than patients. Carers also identified more patient unmet needs than health care professionals, who in turn identified more than patients. Surprisingly, available support did not increase over 6 months and there was a tendency for unmet needs to decrease over time. Low available support, high unmet needs and a larger discrepancy between carer and patients' reports of patients' unmet need predicted negative aspects of caregiver burden. These results suggest that health care professionals underestimate available support to patients and both patients and health care professionals underestimate patients' unmet needs in comparison to carers. Carers' reports of patients' unmet needs are important to consider as they were associated with high levels of caregiver burden, including poorer caregiver health. Health care professionals should encourage opportunities for carers to discuss their views of the ongoing needs of patients with advanced cancer.