The assessment of patient quality of life is assuming increasing importance in medicine and healthcare. In addition to their biological effects, illnesses, diseases and their treatments can have significant impact on mobility, mood, life satisfaction, cognition and the 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. 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 i...