This study examined the external validity of the MMPI Personality Disorder (PD) scales. Patients diagnosed with personality disorders (n = 23), according to a structured interview, were contrasted with medical control subjects and psychiatric patients with no personality disorder (n = 33). The MMPI PD scales could discriminate patients with any personality disorder and patients with specific clusters of personality disorders. Convergent validity was demonstrated by high correlations between the MMPI PD scales and the comparable Millon Clinical Multiaxial Inventory scales, as well as the number of DSM-III personality disorder symptoms. This study represents a preliminary step in the external validation of the MMPI PD scales.