Post-treatment follow-up assessments were conducted on patients from a clinical trial examining the efficacy of different doses of methadone. The Addiction Severity Index (ASI) was administered at treatment entry and ten weeks after the six-month program. Patients were improved in drug and alcohol use, and in areas of pro-social behaviors, at the time of follow-up. Improvements were not related to in-treatment variables, but were related to resumption of treatment during the follow-up interval. These results demonstrate improvement persists after methadone treatment, and further improvement can be achieved by resumption of further treatment.