Introduction: The aim of this study was to compare the characteristics of patients who completed (completers) inpatient treatment of drug dependence with those who failed to complete this programme (noncompleters). Method: Participants were assessed at admission using the Substance Abuse Assessment Questionnaire (SAAQ) to obtain information about the sociodemographic background, history of drug and alcohol use, physical health, mental health, offending behaviour, and interpersonal relationships. Follow-up interviews were carried out 3, 6, 9, and 12 months after discharge using the SAAQ-Follow-up. To form the three comparison groups, participants were divided on the basis of completion of detoxification and receipt of aftercare. Results and conclusions: Significantly better treatment outcome was observed amongst those who completed detoxification and went on to spend at least 6 weeks in a recovery and/or residential rehabilitation unit. In contrast, there were no significant differences between noncompleters and completers who had no aftercare on the majority of measures of drug use during follow-up.