Quality of life measurements are increasingly incorporated into trials of pharmaceuticals. This can be applied to a wide range of medical areas including drug-addiction maintenance treatment programs. Maintenance treatment has been demonstrated to be an effective treatment for opioid addiction but still lacks quality of life specific measures to measure the maintenance program effects and until now there have been only few attempts to assess the impact of opioid dependence and its treatment on the drug-addicted patients' quality of life. The aim of this article is to describe quality of life concept, measurement instruments, selection criteria and its applicability in the drug addiction maintenance studies.