Over the past several years there have been repeated calls for expansion of availability of methadone maintenance in several jurisdictions. Important stakeholders in the expansion of methadone maintenance treatment (MMT) are existing treatment providers. This study describes the impact of the rapid expansion in treatment availability in Ontario on the long-standing MMT program of the Centre for Addiction and Mental Health (CAMH). This expansion occurred through enlarging existing treatment programs, the provision of MMT in private physicians' offices and the establishment of new clinics. With expansion in the community, demand for the clinic-based treatment of the CAMH MMT program did not drop, in fact the patient population was able to continue to grow. There was a broadening of the patient profile in the program including patients who were better educated, more likely to be employed and less likely to be currently injecting (although with a significant history of past injection drug use). Moreover, in the face of these changes, excellent treatment retention was maintained. This suggests that the expansion in treatment availability did not impact negatively on the existing program but rather enabled access for a group of higher functioning opioid dependent patients who were previously being deterred from treatment entry by the large waiting lists and the need for priority access for pregnant and HIV positive heroin users. These findings should provide encouragement for MMT providers in jurisdictions anticipating or undergoing expansion of treatment availability.