Background/Aims: Increasing rates of overdose deaths involving opioid maintenance treatment (OMT) medications and particularly methadone have been observed concurrently with the implementation of liberal OMT strategies (i.e. minimum of control and high doses prescribed). This study examined methadone-related overdose deaths in a liberal OMT programme. Methods: Drug-overdose deaths (n = 130) with detection of methadone in Copenhagen, Aarhus, and Odense Municipality, Denmark, during the period 2008-2011 were identified from a registry. Cases with and without prescribed methadone as OMT were compared. Treatment delivery strategy among OMT-prescribed methadone cases was investigated. Results: Methadone was detected in 130 overdose deaths (71.4% of all overdose deaths). Among these, 63.1% were receiving methadone maintenance treatment. Of these, 79.3% had co-detection of benzodiazepines. Concomitant detection of heroin, non-prescribed benzodiazepines, and younger age were associated with having non-prescribed methadone in the toxicological findings (adjusted OR 3.1, 4.0 and 9.5, respectively). Of the decedents, 43.8% were prescribed a higher methadone dose than recommended (>120 mg daily), of which 80.0% did not have supervised intake of methadone. Conclusions: Liberal OMT access does not necessarily prevent overdose deaths overall. Prescription of higher doses of methadone combined with benzodiazepines may result in an increased risk of overdose for individuals in as well as outside OMT.