To better understand problematic medical patients, the psychiatric diagnoses of 448 patients referred to a behavioral medicine clinic were examined. Forty-two percent met DSM-III-R personality disorder criteria. Analysis of the comorbidity of Axis I and Axis II diagnoses revealed a statistically significant co-occurrence between somatoform and personality disorders (P < 0.0001). Some of the difficulties in making a personality disorder diagnosis are reviewed, as are reasons why knowledge of personality disorder diagnoses is important to medical providers.