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