We conducted a prospective follow-up study of consecutive opiate dependent patients admitted to a residential addiction treatment service for detoxification. We measured the rate of relapse following discharge, and sought to identify factors that were associated with early relapse (i.e., a return to daily opiate use). Follow-up interviews were conducted with 109 patients, of whom, 99 (91%) reported a relapse. The initial relapse occurred within one week in 64 (59%) cases. Multivariate survival analysis revealed that earlier relapse was significantly predicted by younger age, greater heroin use prior to treatment, history of injecting, and a failure to enter aftercare. Unexpectedly, those who were in a relationship with an opiate user had significantly delayed relapse. Those who completed the entire six-week inpatient treatment programme also had a significantly delayed relapse. In order to reduce relapse and the associated increased risk of fatal overdose, services providing residential opiate detoxification should prepare people for admission, strive to retain them in treatment for the full admission period and actively support their entry into planned aftercare in order to improve outcome.