We examine the impact of transfers between methadone treatment prescribing physicians on 1-year retention. Episode data (n=13,359; 1996 to 2001) drawn from a Canadian population-based methadone registry were analysed using a binary logistic regression model. The odds ratios for remaining in treatment for 365 days or more decreased for repeated episodes of treatment, but increased with age and number of transfers. The positive effect of the number of transfers was non-linear and tended to level off with higher numbers of transfers. Analyses indicate that transfers between prescribing physicians may play an important role in prolonging methadone maintenance treatment.