Prototype matching, which involves comparing a patient clinical presentation with a prototype description of the disorder addresses some of the clinical limitations of the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases symptom-count approach. Here, we investigated the validity and clinical utility of three diagnostic systems in predicting patient adaptive functioning using a multimethod multi-informant approach. Specifically, we compared a prototype matching approach based on DSM criteria, an empirically derived prototype matching approach, and DSM symptom count diagnostic systems. A convenience sample of clinicians (N = 80) and patients (N = 170) participated in the study. We imposed minimal exclusion criteria for patient participation to maximize generalizability. Clinicians completed assessment of their active patients using two prototype matching diagnoses, one based on DSM and another that was empirically derived. Independent interviewers completed the Structured Clinical Interview to provide DSM symptom count. Patient global composite assessment of adaptive functioning, rated across the clinician, patient self-report, and independent interviewer, served as outcome variable. Prototype diagnosis for personality disorders, both one that is based on DSM criteria and one that was empirically derived, demonstrates some incremental validity over and above the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition symptom count, in predicting patient's adaptive functioning. Specifically, avoidant personality disorder prototype diagnosis significantly contributed to prediction of adaptive functioning. Furthermore, clinicians rated the prototype-matching approach as more useful in clinical practice compared with the current DSM-IV categorical approach. Using a dimensional approach, which is based on prototype matching that also preserves the advantages of categorical system offers a valid and efficient approach to psychiatric assessment for personality disorders. (PsycINFO Database Record (c) 2019 APA, all rights reserved).