The assessment of patients’ quality of life is assuming increasing importance in medicine and health care. Illnesses, diseases and their treatments can have significant impacts on such areas of functioning as mobility, mood, life satisfaction, sexuality, cognition, and ability to fulfil occupational, social and family roles. The emerging quality of life construct may be viewed as a paradigm shift in outcome measurement since it shifts the focus of attention from symptoms to functioning. This holistic approach more clearly establishes the patient as the centre of attention and subsumes many of the traditional measures of outcome. Quality of life assessment is particularly relevant to patients with progressive conditions, particularly in the later phases of the disease. Despite the fact that current definitions of palliative medicine include quality of life as a central concern, relatively little research has been conducted on the impact of palliative care on patient quality of life. This paper introduces the concept of quality of life and describes the significant difficulties in definition, measurement and interpretation that must be addressed before such measures can be used as reliable and valid indicators of disease impact and treatment outcomes. It is argued that the unique individual perspective of the patient on his or her own quality of life must be incorporated into outcome assessments aimed at improving the quality of health care delivery in progressive diseases.