One expression of the complex relationship between personality and affective disorder is the comorbidity of personality disorders (PDs) with affective disorders. In a sample of 117 patients with unipolar and 60 with bipolar affective disorders, we assessed DSM-III-R PDs with the Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II) and compared them with personality factors as obtained by the five-factor model (FFM-NEO Five-Factor Inventory). Fifty-one percent of the unipolar and 38% of the bipolar disorders fulfilled criteria for a comorbid PD. The three most frequent PDs were obsessive-compulsive PD, borderline PD, and narcissistic (bipolar) or avoidant (unipolar) PD. Cluster C PDs and especially avoidant PD occurred significantly more frequently in unipolar than in bipolar patients, while narcissistic PD occurred significantly more often in bipolar than in unipolar patients. The FFM results supported the validity of our PD diagnoses. In a logistic regression analysis, higher depression score at the time of the SCID-II interview and shorter duration of the illness were weakly related to a higher frequency of PDs. Our results indicate that PDs are frequent in affective disorders and that there are subtle differences between unipolar and bipolar patients concerning such comorbid disorders.