Abstract: Despite evidence that methadone maintenance treatment (MMT) is effective for opioid dependence, it remains a controversial therapy which its effectiveness has been disputed. The aim of this study was to compare the effectiveness of MMT vs. narcotics anonymous (NA). This was a longitudinal follow-up study. A total of 600 patients were included. The patients, current opioid misuse was confirmed by rapid urine test. Three hundred cases were engaged in MMT and others in NA program. The patients were not randomized to conditions but the groups were balanced. The study protocol consisted of a basic interview with the patients. Follow-up visits were scheduled. The goal of the study was to compare the outcomes of two groups regarding the retention rate. The majority of clients were male in both groups. The median age was 34 years in MMT group and 30 years in NA group. The median duration of opioid misuse before beginning the treatment was 7 and 2 years in MMT and NA groups. Seventy-four percent and 84% of patients remain in treatments in MMT and NA groups, respectively. The mean number of days in treatment was 210 days in MMT group compared to 270 days in NA group. There was no significant difference between 2 groups in this regard. Our findings suggest the usefulness of MMT in reducing opioid misuse but it does not show a statistically significant superior effect on key outcomes, including retention in the treatment.