A sample of 183 current methadone maintenance patients were interviewed on their drug use history, criminal history, current drug use, and symptoms of Anti-social Personality Disorder (ASPD). Thirty-nine percent of patients met the DSM-III-R criteria for a diagnosis of ASPD. ASPD patients had an earlier onset of drug use, drug injecting, heroin use, had wider polydrug using histories and had been arrested earlier and more frequently than other patients. Despite the different pretreatment histories of ASPD and other patients, there were no differences between the two groups in retention in treatment, methadone dosage or heroin use. It is concluded that heroin-dependent ASPD patients can be successfully retained in methadone treatment, on similar methadone doses and with similar in-treatment drug use patterns as those of non-ASPD heroin dependent patients.