Differences between the opioid addiction careers of 84 female and 91 male addicts were examined longitudinally. Data were collected from clients participating in methadone maintenance treatment programs between 1969 and 1972 as part of the Drug Abuse Reporting Program (DARP). Clients were interviewed prior to and during treatment, as well as 6 and 12 years after treatment. No differences between male and female addicts were found for demographic characteristics or treatment histories. Further, differences in behavioral outcomes for criminality and employment found at 12-year follow-up were shown to be a function of pretreatment differences, and were not related to differential treatment effects. Males and females did differ, however, in psychological status at 12-year follow-up, and in their reasons for quitting drug use and entering treatments. These differences, along with significantly greater financial and medical needs for females, indicate systematic long-term differences between female and male addiction careers which should be considered in prevention and treatment of opioid addiction.