Summary Although the need for a method of measuring the quality of life of patients undergoing therapy for cancer has been widely recognised, no adequately evaluated or feasible method has been established. We describe a method in which 31 items were assessed by patient self report using linear analogue scales. Eighteen items inquiring about general health problems were derived from the Sickness Impact Profile, an established method of assessing the effect of health upon behaviour and function. Thirteen items inquiring about major problems associated with breast cancer were derived from clinical experience and the opinions of patients with this disease.Each item of the measurement method (instrument) has been evaluated for content, feasability, reliability and validity by methods that are widely used in psychometry but less familiar in medicine. It appeared easy to use, acceptable and reliable in these assessment. Validity was evaluated indirectly since no standard measurements of quality of life exist for comparison. Most items appeared valid when compared to alternative measurement methods including the Sickness Impact Profile and evaluation by a physician in a structured interview. The correlations between items in the instrument were analysed by factor analysis and seemed to fit with the clinical features of breast cancer. The method distinguished between clinically distinct groups of patients and detected changes with time.The study illustrates the possible approaches to the scientific evaluation of methods for measuring subjective features of patients lives. This method appears suitable for some purposes to measure quality of life in breast cancer and is intended to be flexible enough to be modified for other diseases. However, further evaluation, development and refinement will be needed before routine clinical application can be recommended.