This study was conducted to assess changes in health-related quality of life over a 3-year follow-up period in a cohort of 135 opioid dependent patients using the Nottingham Health Profile (NHP) questionnaires. Data obtained at 12 months from 80 patients retained in the programme are presented. In summary, opioid addicts in a methadone maintenance programme for a 12-month period experienced an early and substantial improvement in health-related quality of life. The use of the NHP questionnaire to monitor changes in the subjective health of opioid-dependent patients over time provides new insights in the assessment of treatment effectiveness of methadone maintenance programmes.