Ageing populations increasingly face chronic and terminal illnesses, emphasising the importance of palliative care and quality of life for terminally ill people. Facing resource constraints in professional healthcare, some governments expect informal caregivers like volunteers to assume a greater share of care provision. We know volunteers are present in palliative care and perform many roles, ranging from administration to providing companionship. However, we do not know how involved they are in the organisation of care and how healthcare organisations appraise their involvement. To address this, we provide an extensive description of the involvement of volunteers who provide direct patient palliative care across the Flemish healthcare system in Belgium. We conducted a cross-sectional postal survey of 342 healthcare organisations in Flanders and Brussels in 2016, including full-population samples of palliative care units, palliative day care centres, palliative home-care teams, medical oncology departments, sitting services, community home-care services, and a random sample of nursing homes. Volunteer involvement was measured using Sallnow and Paul's power-sharing model, which describes five hierarchical levels of engagement, ranging from being informed about the organisation of care to autonomy over certain aspects of care provision. Response was obtained for 254 (79%) organisations. Volunteers were often informed about and consulted regarding the organisation of care, but healthcare organisations did not wish for more autonomous forms of volunteer involvement. Three clusters of volunteer involvement were found: "strong involvement" (31.5%), "restricted involvement" (44%), and "uninvolved" (24.5%). Degree of involvement was found to be positively associated with volunteer training (p<0.001) and performance of practical (p<0.001) and psychosocial care tasks (p<0.001). Dedicated palliative care services displayed a strong degree of volunteer involvement, contrary to generalist palliative care services, suggesting volunteers have a more important position in dedicated palliative care services. A link is found between volunteer involvement, training, and task performance.