Quality of life is becoming recognized increasingly as an important outcome measure which needs to be considered by social workers. However, there does not appear to be a clear consensus about the definition of quality of life. In addition, social workers are likely to experience difficulties choosing and applying an appropriate instrument with which to measure quality of life because of the many available instruments purporting to assess quality of life. This paper discusses the definition of health-related quality of life and explains the main measurement properties of an instrument that must be appraised when considering whether or not an instrument is appropriate. The paper will assist social workers to make an informed choice about measures of health-related quality of life.