This article summarizes some of the methodologic and practical issues relevant to health related quality-of-life (HRQL) assessment in randomized clinical trials. Particular attention is given to 1) the reasons for undertaking HRQL assessment, 2) the types of clinical trials particularly suitable for HRQL assessment, 3) the selection of appropriate HRQL measures, 4) statistical issues in the design and analysis of HRQL studies, and 5) the need to coordinate progress in HRQL studies in clinical research.