Although many clinicians have long believed that personality pathology may interfere with the effectiveness of treatment of axis I disorders, until recently there were no empirical studies on the subject. This report reviews the recent literature with regard to the following questions: a) Does personality pathology predict negative outcome of treatment for axis I disorders? b) If so, are there specific personality traits or disorders that account for such a negative outcome? The literature review reveals a robust finding that patients with personality pathology have a poorer response to treatment of axis I disorders than those without such pathology. Specific axis I disorders reported on include DSM-III major depression, panic disorder, and obsessive-compulsive disorder. Both inpatients and outpatients have been studied. There is too little literature to determine whether certain pathological personality traits are especially important, but there is enough to provide methodological guidance for future studies. Such studies should use standardized measures of personality and outcome, should match personality and nonpersonality groups on severity of the axis I disorder, and should be certain that axis I diagnoses are not confounded by axis II symptoms.