Health-related quality of life is increasingly accepted as a relevant endpoint in medicine. Available work pertains to development and psychometric testing of measurement instruments. Theoretical papers are largely missing. However, inclusion of instruments in clinical trials has just begun, especially in oncology and cardiology. Based on a review of available literature, areas of applying of quality of life research are described. Foci of attention are conceptual, methodological and practical challenges, as well as the contribution of quality of life research to assessing the results of medical treatment.