The Minnesota Multiphasic Personality Inventory-2 Restructured Form (MMPI-2-RF) is an alternative version of the MMPI-2 and is useful for the differential diagnosis of psychiatric disorders. This study sought to assess the relationship between MMPI-2 Scale scores and psychiatric diagnoses, and to identify the scales that best predicted that a diagnosis would be assigned. The sample was comprised of participants who were administered the MMPI-2 between 2001 and 2010 at a university-based psychological services center, and participants were divided into diagnostic categories based on Diagnostic and Statistical Manual of Mental Disorders–Fourth Edition, Text Revision diagnoses. Categories with enough participants to conduct statistical analyses were examined; these categories included participants who were diagnosed with substance-related disorders, depressive disorders, anxiety disorders, and participants who were not given a psychiatric diagnosis. The Substance-Related Disorders category was not significantly correlated with any scale but was best predicted by Cynicism (RC3) and Substance Abuse (SUB). The Depressive Disorders category was significantly correlated with Emotional/Internalizing Dysfunction (EID), Demoralization (RCd), Low Positive Emotions (RC2), and Self-Doubt (SFD) Scales, and was best predicted by RCd. The Anxiety Disorders category did not significantly correlate with any scale but was best predicted by Infrequent Somatic Responses (Fs) and Gastrointestinal Complaints (GIC). The No Diagnosis category was negatively correlated with Infrequent Responses–Revised (F-r), EID, RCd, Helplessness/ Hopelessness (HLP), and Cognitive Complaints (COG), and was best predicted by EID. This study offers important information regarding scales that best predict psychiatric disorders and adds to the research that suggests that the MMPI-2-RF can aid clinicians in the differentiation of psychiatric disorders.