Quality of Life (QoL) is the main goal of palliative care according to the definition of the World Health Organisation. However, there is no consensus on how to define or assess QoL. There are philosophical arguments against assessment of QoL such as impossibility of quantification, individuality and subjectivity. Calman defined QoL as the difference between reality and expectations. The modification of expectations could be an interesting strategy for palliative care.
Conceptually there are two different approaches to define QoL: the so-called "health-related" QoL, exemplified by measures such as the Sickness Impact Profile (SIP) and the Short Form-36 (SF-36), and the individual QoL, exemplified by the Schedule for the Evaluation of Individual QoL-Direct Weighting (SEIQoL-DW). The former questionnaires are heavily weighted toward functional status, thus confronting patients with terminal diseases with their progressive loss of function. Since they are based on a fixed, external, function-based value system, HRQoL questionnaires may not reflect the patients‘ individual perception of QoL accurately. The SEIQoLDW, an instrument to measure the individual QoL allows the patients to name the five most relevant domains which present his QoL, rate his satisfaction with each domain and weight the domains against each other. Satisfaction and weighting of domains are summed up in a total QoL score. With the SEIQoL-DW it is possible to show longitudinal changes and thus coping strategies. Data from patients with motor neuron disease show that health status is overestimated and that the role of the family is preeminent. There is no gold standard to assess quality of life in palliative care. The choice of the instrument depends on the intention of the measurement. If the intervention is aimed at improving symptom control, disease and symptom specific tools should be used. If the overall impact of palliative care is the main outcome, and particularly when the focus is on psychosocial aspects, indidual QoL instruments should be considered. Assessment of QoL in palliative care is incomplete if the family is not included.