Clinicians, regulatory authorities, and pharmaceutical companies increasingly recognize the importance of assessing the patient's perspective on the impact of disease and its treatment on their health-related quality of life (HRQoL). This article describes the importance of assessing HRQoL, particularly in patients with chronic disease, provides examples of the different types of instrument available for measuring HRQoL and considers how such assessment can aid medical-decision making. In addition we consider the potential role of HRQoL assessment in routine clinical practice, and its use in licensing and health technology appraisal.