The purpose of this study was to assess the psychometric properties of the Zanarini Rating Scale for Borderline Personality Disorder (ZAN-BPD), the first clinician-administered scale for the assessment of change in DSM-IV borderline psychopathology. The questions for the measure were adapted from the BPD module of the Diagnostic Interview for DSM-IV Personality Disorders (DIPD-IV) to reflect a 1-week time frame and each of the nine criteria for BPD is rated on a five-point anchored rating scale of 0 to 4, yielding a total score of 0 to 36. Two diagnostic interviews that assess the presence of BPD were administered to 200 nonpsychotic patients: the BPD module of the DIPD-IV and the Revised Diagnostic Interview for Borderlines (DIB-R). The ZAN-BPD was also administered, blind to diagnostic information. In addition, each patient filled out a self-report measure of general psychopathology that is often used in borderline treatment studies, the Symptom Checklist 90 (SCL-90). The convergent validity of the ZAN-BPD and relevant scales of the SCL-90 and the DIB-R was assessed and found to be highly significant. The discriminant validity of the various scores of the ZAN-BPD was also found to be highly significant, easily discriminating the 139 patients who met the DSM-IV criteria for BPD from the 61 patients who did not. In addition, internal consistency of the ZAN-BPD was found to be high (Cronbach's alpha=0.85). The interrater reliability of the ZAN-BPD was assessed using 32 conjoint interviews, while same day test-retest reliability was assessed in a separate sample of 40 patients. All reliability raters were blind to all previously collected information concerning each subject. All intraclass correlations were in the good to excellent range. Finally, the sensitivity of the ZAN-BPD to change was assessed using a third sample of 41 patients who were reinterviewed by a blind rater 7 to 10 days after the ZAN-BPD was first administered. The SCL-90 was also readministered at this time. The correlations between difference scores of the ZAN-BPD and difference scores of the SCL-90 were found to be significant, indicating that the ZAN-BPD measures change in a clinically meaningful manner. Taken together, the results of this study suggest that the ZAN-BPD is a promising clinician-administered scale for the assessment of change in borderline psychopathology over time.