No clinician-rating tool has formally been developed to assess the ICD-11 model of personality disorder (PD) severity. We therefore developed and evaluated the 14-item personality disorder Severity ICD-11 (PDS-ICD-11) Clinician-Rating Form. A combined sample of 195 patients was rated by mental health professionals or clinical research assistants in New Zealand using the PDS-ICD-11 Clinician-Rating Form. Responses were subjected to item-response theory analysis and confirmatory factor analysis. In a subsample, we examined interrater reliability and convergence with self- and informant-reported measures of personality impairment, dysfunction in various psychopathology domains, and traditional PD symptoms. Item-response theory and confirmatory factor analyses supported the item functioning and unidimensionality, respectively, of the PDS-ICD-11 Clinician-Rating Form. The interrater reliability was very promising (intraclass correlation coefficient = 0.94, p < 0.001). PDS-ICD-11 Clinician-Rating Form scores were associated with established measures of personality dysfunction at large effect sizes. This initial development study suggests that the PDS-ICD-11 Clinician-Rating Form constitutes a psychometrically sound instrument that provides a clinically based impression of the severity of personality dysfunction according to the official ICD-11 description. More research is needed to corroborate its validity and utility, and a structured interview is warranted for diagnostic purposes. The final PDS-ICD-11 Clinician-Rating Form is included as online supporting information.