Previous evidence on the effectiveness of treatment for PD has been mixed and little data exists concerning the treatment of PD in offender populations. Despite the paucity of data, the Netherlands remains committed to treating offenders with PD in specialized forensic hospitals. The current study evaluated the effectiveness of residential treatment for criminal offenders suffering from PD. The hypothesis was that the residential treatment for PD offenders would produce positive changes in personal disorder pathology. Participants were 59 offender patients who completed the Structured Interview for DSM Personality Disorders (SIDP-R) and the Personality Diagnostic Questionnaire-Revised (PDQ-R) at in-take. Following 2 years of intensive, inpatient treatment, participants were reassessed using self-report questionnaires. Results indicated a significant decrease in personality disorder pathology at follow-up, as measured by the PDQ-R. Over one-quarter of the participants improved to a reliable and clinically significant extent and nearly 40 percent improved reliably across personality disorder features. One limitation of the research is that the evaluation was unable to ascertain whether the changes implied a substantial reorganization of personality or whether the change occurred at a more superficial level. Future research should incorporate a longer follow-up time to ascertain changes following hospital release. Tables, figure, references