Reduction of mortality is a basic goal of methadone maintenance treatment (MMT) for opioid addicts. During the last years, however, there have been reports about drug related deaths of MMT patients and of untreated drug addicts who had consumed illegally purchased methadone. To evaluate the supposed beneficial effect of MMT on mortality, data from a multicentre trial in the German state of North Rhine-Westphalia were analysed. 244 patients with long histories of opioid addiction and previous failures in at least two abstinence oriented treatments were observed for at least four years and up to eight years after admission to MMT. With 32 deaths out of 244 participants, the mortality rate for the whole sample was 2.5 % p.a. This rate is not remarkably different from estimations for opioid addicts in general. However, addicts in continuous maintenance treatment had a mortality rate of only 1.6 % p.a., in contrast to a rate of 8.1 % p.a. for addicts who had left treatment. These results are supported by other long-term studies with large patient samples. Therefore it is concluded that methadone maintenance treatment is a measure to reduce the mortality in opioid addicts. Attainment of this goal is threatened, however, by deviations from safety standards, especially if take-home privileges are granted too widely.