It is well known through research that crime correlates with drug abuse, a relationship that is reciprocal. Such information has been found in studies made by criminologists like Trevor Bennett (2005). Vital conclusions by researchers have made maintenance treatment for opioid-addiction well renowned for its effectiveness. This is the background for this thesis; to explore the effectiveness of maintenance treatment in crime reduction. With the methodological guidance of Willman and Stoltz (2002) research-data has been obtained, mainly through their seven-step-model. This systematic review contains ten articles that are all randomized controlled trials that were derived from the database PubMed. Results from these studies showed a decrease in crime during and after maintenance treatment. It is also presented, that using buprenorphine in the treatment increased the retention grade of patients in comparison to methadone. With this in mind we ask the question, why do not other substances than methadone have a more frequent usage in the aspects of maintenance treatment?