The pharmaceutical industry, the medical device industry, and national regulatory agencies such as the United States Food and Drug Administration (FDA) are faced with a number of difficult issues related to the development and evaluation of health-related quality of life (HRQL) claims for product labeling and promotion. This paper outlines some of the unique challenges of HRQL research and makes recommendations for assuring that claims are based on the results of rigorous studies designed and conducted according to accepted scientific principles and practices. Standards of evidence for HRQL are discussed in terms of research design and methodology, instrumentation, statistical analysis, and interpretation. Examples are provided to highlight important points. The paper concludes with a brief discussion of future trends in HRQL outcomes evaluation.