Approximately 4.5 to 6.3 million youth experience serious emotional disturbances. Unfortunately, many of them have unmet mental health needs. Tools used in personality assessment can offer unparalleled assistance in diagnosis, and assist in designing appropriate interventions. Unfortunately, not all psychologists embrace personality assessment as a key component in conducting a comprehensive psychological evaluation. In this article the effective use of personality assessment tools is described, with particular attention to issues of comorbidity. Guidelines for effective practice are also offered.