Although interest is increasing in measurement of quality of life, health status, and functional status in clinical research, most often the primary focus of the research is traditional measures of mortality and morbidity. Quality-of-life assessments are usually added as an afterthought once the design, data collection, and analytic techniques have been specified. When nonmedical outcomes are considered, they are thought of as quality-of-life outcomes. Quality of life is not well conceptualized in the medical and health literature. In addition, clinical researchers are searching for a single best measure of quality of life. Lack of information about clinical significance and sensitivity and uncertainties about the advantages of different administration strategies are impediments to use of developed measures. These issues and problems are discussed and suggestions made about procedures and investigations that could provide guidance.