This is the first of a two-part paper on quality of life in cancer patients. This part examines some of the fundamental issues in health-related quality of life measurement with particular attention being given to cancer medicine, thus helping to focus the direction and methodological rigour required in future investigations. Relevant topics are discussed to illustrate the importance of quality of life measures in cancer care. A perspective on the meaning of "outcome' and "quality of life' are presented to demonstrate the controversies that exist in the field. It is concluded that despite methodological limitations, quality of life measures have a potential role in advancing cancer care.