summary On the basis of repeated REHAB measurements (rehabilitation Evaluation Hall And Baker), behavioural changes during forensic psychiatric treatment in de Kijvelanden are evaluated. In addition, this study explores whether psychotic patients' behaviour improves faster or slower, as compared to non-psychotic counterparts. It is found that, in general, the behaviour of forensic psychiatric patients improves during hospitalisation. The question whether this clinically observed progress is associated with an actual decrease of criminal activity after discharge cannot be answered with the present study design. Compared to non-psychotic patients, patients suffering from psychoses show no improvement on the REHAB during the admission. Therapy resistance and/or non-compliance, however, are likely to be relatively prevalent phenomena in this group of psychotic offenders.