Objective: Borderline personality disorder (BPD) is characterized by a high frequency of comorbidity with major depressive disorder (MDD). This study aimed to compare the clinical characteristics of 2 groups of patients with MDD: those with concomitant BPD and those with other concomitant personality disorders. Methods: We assessed 119 outpatients, using a semistructured interview for demographic and clinical features, the Structured Clinical Interview for DSM-IV, Hamilton anxiety and depression scales, the Zung Self-Rating Depression Scale (ZSDS), the Social and Occupational Functioning Assessment Scale (SOFAS), the Sheehan Disability Scale, and the Revised Childhood Experiences Questionnaire. We performed a regression analysis, using the number of criteria for BPD as the dependent variable. Results: Severity of BPD was positively related to the ZSDS score, to self-mutilating behaviours, and to the occurrence of mood disorders in first-degree relatives; it was negatively related to the SOFAS score and age at onset of MDD. Conclusions: Patients with comorbid NIDD and BPD present differential characteristics that indicate a more serious and impairing condition with a stronger familial link with mood disorders than is shown by depression patients with other Axis II codiagnoses.