Abstract: Aim of the Study: To assess the long-term hepatitis C (HCV) treatment outcome in former injecting drug users (IDUs). Materials and Methods: A long-term follow-up of 27 former IDUs who had been successfully treated for chronic hepatitis C was performed. These patients represented ailiDUs who had obtained a sustained virological response in a Norwegian HCV treatment trial. The patients had been treated with interferon-a alone or in combinatlon with ribavirin. At 5 years’ follow-up the 27 IDUs were retested for HCV RNA and risk behaviour for HCV transmission after treatment was assessed. In the control group ail 18 non-IDUs who had obtained a sustained virological response in the same treatment trial were included. Results: At follow-up 13-82 months (median 64) after the end of treatment only one case of probable reinfection was seen among the 27 IUDs. No reoccur- rence of HCV was observed in the control group. The IDU who was HCV RNA positive at follow-up had continued injecting drugs and reported frequent needle sharing. At follow-up HCV of genotype 1a was detected in contrast to genotype 1b before treatment indicating that this patient was reinfected with HCV. A return to injecting drug use occurred in 9 (33%) of 27 IDUs. Conclusion: The long-term outcome of HCV treatment in former IDUs was excellent. Despite frequent reinitiation of drug injection ail but 1 remained HCV RNA negative.