AbstractThe development of standardized instruments to evaluate treatment outcome for opioid dependence is necessary to determine individual patients' progress within a particular treatment programme and to compare treatment outcomes across programmes. This paper reports the results of an inter‐rater reliability study utilizing the Opiate Treatment Index (OTI). The OTI questionnaire is a standardized opiate treatment evaluation tool developed within a research setting. The main aim of this study was to determine within the clinical setting of a Methadone Treatment Programme (MTP), whether information given by patients differed significantly according to whether the OTI questionnaire was administered by clinicians working within the service, or by an unknown research assistant. Results indicated that overall there were few differences between the information given to clinicians compared with that given to the research assistant and that in general, inter‐rater reliability was good. A number of issues related to the development and use of treatment outcome measures in clinical settings are highlighted and it is proposed that for MTPs a shorter questionnaire, based on the OTI, be develo