The authors sought to determine whether a 5-point global rating of personality dysfunction on the Level of Personality Functioning Scale proposed as a severity index for Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), would be related to DSM-IV personality disorder diagnosis as well as to other key clinical judgments. Data were collected from a national sample of 337 mental health clinicians who provided complete diagnostic information relevant to DSM-IV and proposed DSM-5 personality disorder diagnoses, as well as demographic information and other clinical judgments, on one of their patients. Of the 337 patients described, 248 met criteria for 1 of the 10 specific DSM-IV personality disorders. A “moderate” or greater rating of impairment in personality functioning on the Level Scale demonstrated 84.6% sensitivity and 72.7% specificity for identifying patients meeting criteria for a specific DSM-IV personality disorder. The Level of Personality Functioning Scale had significant and substantial validity correlations with other measures of personality pathology and with clinical judgments regarding functioning, risk, prognosis, and optimal treatment intensity. Furthermore, the single-item Level of Personality Functioning rating was viewed as being as clinically useful as the 10 DSM-IV categories for treatment planning and patient description and was a better predictor of clinician ratings of broad psychosocial functioning than were the 10 DSM-IV categories combined. These results confirm hypotheses that the single-item Level of Personality Functioning Scale rating provides an indication of severity of personality pathology that predicts both assignment of personality disorder diagnosis and clinician appraisals of functioning, risk, prognosis, and needed treatment intensity.