BACKGROUND: Chronic pain is highly prevalent among people in methadone maintenance treatment (MMT) for opioid use disorder and is known to be an important contributor to treatment discontinuation and opioid relapse. Mindfulness-Oriented Recovery Enhancement (MORE) is one of the few interventions developed and tested as an integrated treatment to simultaneously address both pain and illicit opioid use; however, this study is the first to evaluate MORE as an adjunct to MMT. METHODS: Randomized individuals in MMT (N = 30) received MORE plus methadone TAU (n = 15) or methadone TAU, only (n = 15). Participants in the MORE arm received their MMT, as usual, and attended eight, weekly, two-hour MORE groups at their MMT clinics. Participants in the TAU arm received their MMT, as usual, and group or individual counseling, as required by the clinic. TAU counseling consisted of relapse prevention, cognitive-behavioral therapy, and supportive treatment. TAU participants did not receive any mindfulness-based intervention. Participants completed assessments at baseline, post-treatment (i.e., 8-weeks post-baseline), and follow-up (i.e., 16-weeks post-baseline). RESULTS: Participants in MORE evidenced significantly fewer baseline adjusted days of illicit drug use and significantly lower levels of craving through 16-week follow-up compared to TAU. Also, Participants in MORE reported significantly lower levels of pain, physical and emotional limitations, depression, and anxiety through 16-week follow-up compared to TAU. Conversely, participants in MORE reported significantly higher levels of well-being, vitality, and social functioning through 16-week follow-up compared to TAU. CONCLUSION: MORE could be an effective adjunct to MMT, and larger trials are warranted.