AIM: To evaluate the efficacy of naltrexone maintenance treatment in preventing relapse in opioid addicts after detoxification. DESIGN: A systematic review according to the methodology developed by the Cochrane Collaboration based on either randomized controlled trials (RCTs) or controlled clinical trials (CCTs). PARTICIPANTS: Seven hundred and seven heroin dependent in-and out-patients, or former heroin addicts dependent on methadone and participating in a naltrexone treatment programme; 89% were male. INTERVENTION: Maintenance treatments on opiate dependent people after detoxification, comparing naltrexone with placebo, pharmacological or behavioural treatments. MEASUREMENTS: The outcomes considered were successfully completed treatment, opioid use under treatment (re)-incarcerations during the study period, mean duration of treatment. FINDINGS: The outcomes tended to be slightly although not significantly in favour of the naltrexone groups. Use of naltrexone in addition to behavioural treatment significantly decreased the probability of (re-) incarceration (OR= 0.30; 95% CI 0.12, 0.76). The difficulties in producing a quantitative analysis were due mainly to the heterogeneity of the included studies. CONCLUSIONS: From the available clinical trials performed up to this time, there is insufficient evidence to justify the use of naltrexone in maintenance treatment of opioid addicts.