To describe consequences of the presence of a comorbid personality disorder (PD) in inpatients with a major depressive disorder (MDD) on variables connected to course and outcome of the unipolar affective illness, 117 inpatients with a major depressive episode were assessed at various times during inpatient treatment. Trait markers (including personality and PDs) were obtained toward the end of the treatment, when acute psychopathology had largely remitted. Fifty-one percent of all patients fulfilled the criteria for a DSM-III-R PD, 15% met the criteria for two or more PDs, and 18% fulfilled the criteria for at least one cluster A or B PD. Except for age of onset, number of suicide attempts and quality of life all other outcome and course variables were unrelated to the presence or absence of a comorbid PD. In this sample, one comorbid PD in patients with MDD was of limited relevance to the course of the affective illness, especially if it was a cluster C PD. Two or more comorbid PDs in patients with unipolar depression tended to reduce quality of life and have an earlier age of onset. Patients with cluster A or B PD and MDD had attempted suicide more often than patients with a cluster C PD and MDD. Although comorbid cluster C PDs were seen in all age groups of patients with an MDD, cluster A or B PDs and the presence of more than one PD were mainly seen in younger patients with an MDD.