In clinical trials, the assessment of health-related quality of life (QOL) (or patient-reported outcome [PRO] measure) has become very popular especially for clinical studies conducted for evaluating clinical benefits of patients with chronic, severe, and/or life threatening diseases. Health-related QOL information and PRO measures are useful for disease management for achieving best clinical practice. In this article, we will focus on health-related QOL assessment. The concept, design, and analysis of health-related QOL in clinical trials are reviewed. Validation of the use of health-related QOL instrument in terms of some key performance characteristics such as accuracy, reliability, sensitivity, and responsibility for assuring quality, integrity, and validity of collected QOL data are discussed. The concept of utility analysis and calibration (e.g., with respect to life events) for achieving the optimization of disease management are proposed. The change of the QOL could be translated into different life events for effective disease management. These translations could evaluate the treatment effect by more directly displaying the change of the QOL.