This review article summarizes the results of all available clinical trials considering the use of slow-release oral morphine (SROM) for opioid maintenance treatment (OMT). All studies published up to October 2010 and assessing SROM for OMT in adult patients are included. Three independent reviewers assessed the selected articles using a standardized checklist. Study design, study length and number of subjects included were recorded. Data about retention rate (proportion of participants remaining under maintenance treatment at the end of the study), quality of life, withdrawal symptoms, craving, additional drug consumption, driving capacity and adverse events were collected. We identified 13 articles corresponding to nine clinical trials considering the use of SROM for OMT. Among them, only one was a randomized trial and one was a controlled not randomized trial. All other studies were uncontrolled. Retention rates were good (from 80.6 to 95%) with SROM maintenance, but similar retention rates were obtained with methadone. Most of the studies showed that quality of life, withdrawal symptoms, craving and additional drug consumption improved with SROM. However, there was no comparison with other maintenance drugs. As most of the studies assessing SROM efficacy were uncontrolled, there is no definite evidence that SROM is an effective alternative to methadone for OMT.