Objective: In Malaysia, opioid abuse is an acknowledged problem with severe health and economic repercussions. Until recently, drug addicts were mainly criminalised and forcefully rehabilitated in correctional facilities. However, the high relapse rates of this approach, coupled with the high rates of blood borne infections among drug users, led to increasing acceptance of a healthcare-based approach in the rehabilitation of drug addicts. Methadone was among the medications introduced as substitution maintenance therapy in 2005 and Universiti Malaya Medical Centre (UMMC) is a centre for MMT. This study aimed to determine the effects of MMT on quality of life in patients here. Methods: The sample was 46 patients who attended the Psychiatric outpatient clinic in fill in UMMC. The instrument used to assess quality of life was the WHOQOL-BREF. Results: The study design was cross-sectional with retrospective elements. Baseline QOL scores were obtained from case records and follow-up scores from the month of September 2007. Statistically significant improvements in all four domains of WHOQOL-BREF were found. Physical: p<0.01, C.I. 1.46-3.05. Psychological: p<0.01, C.I. 1.44-3.11. Social: p=0.03, C.I. 0.66-3.05. Environmental: p<0.01, C.I. 0.85-2.24. Conclusion: Methadone maintenance therapy substantially improves quality of life in ex-opioid abusers.