BACKGROUND: Opioid substitution therapy (OST) was officially introduced in Austria in 1987. Over the years coverage increased to 50 to 60 percent of all problem opioid users. METHODS: Data of the pseudononymised substitution registry was used to analyse treatment duration. Linkage to pseudononymised criminal records were used to gather insight into stability of long term OST patients. RESULTS: One third of clients starting OST in 1990 was still or again in OST after 23 years. Almost two thirds of patients starting OST in 2003 were still or again in OST after 10 years. While over 10 percent of OST patients with treatment duration below one years were found in the criminal records of 2013 only 5 percent of patients with treatment duration of more than 9 years were notified by the police. CONCLUSIONS: Opioid addiction is a long term chronical disease. Stability increases with OST duration but even a small part of OST patients with treatment duration of more than 9 years relapse to criminal activity.