Completion of treatment is an important predictor of favourable outcome. We need more knowledge about predictors of completion in the inpatient psychosocial treatment modality. This prospective study from 13 such programmes follows a consecutive sample of clients (n = 307) from admission to completion/dropout. Instruments: EuropASI, MCMI II, SCL-25. The mean completion rate was 40% (20-71%), with no difference between clients with no ('debutants') or previous ('veterans') inpatient stays. Among 'debutants', the number of years of heroin use was negatively related to completion. Among 'veterans', age and amphetamine use were positively related, while the presence of a personality disorder and number of previous inpatient treatments were negatively related to completion. Specific strategies for involving clients with personality disorders are needed. After three inpatient stays, other types of treatment should be offered.