OBJECTIVES: This comparative study investigated consumption patterns, comorbidity and treatment utilization of opioid addicts in six European cities (Athens, Essen, London, Padua, Stockholm, Zurich). SUBJECTS AND METHODS: Data were collected by structured face-to-face interviews. The representative sample comprises 599 addicts (100 patients per centre, 99 in London) at the start of a treatment episode. RESULTS: Patients were dependent on opioids for about 10 years. Regional differences were significant regarding the patients' drug consumption pattern and their method of heroin administration (up to a fourth of the patients in Essen, London and Zurich usually smoke heroin). Concomitant use of benzodiazepines, cannabis and alcohol was common in all regions with the German and English samples showing the highest level of polydrug use. The prevalence of major depression was high in all regions (50%). Stockholm and London patients worry most about their physical health. Differences in the amount of needle sharing and especially in the use of public health service were prominent between the sites. Opioid addiction was a long-term disorder associated with a high burden of comorbidity and social problems in all cities. CONCLUSION: The results of the study show significant interregional differences of opioid addicts which might require different treatment strategies in European countries to handle the problem.