Avoidant personality disorder (APD) and borderline personality disorder (BPD) are the most frequent personality disorders (PDs) in clinical practice. Although BPD research dominates the field, both PDs are clearly associated with severe functional impairments and substantial treatment challenges. Few have investigated the relationship between core personality vulnerabilities across PDs. However, such research has high clinical relevance, could expand our understanding of the distinct nature of the disorders, and thus have important therapeutic implications. Central PD vulnerabilities have been conceptualized in two, possibly overlapping, constructs: mentalization and affect consciousness (AC). The interrelationship between mentalizing and AC and PD specific differences are, as yet, not well established. The present study investigated the relationship between mentalizing capacity and AC among 73 treatment-seeking patients with APD and/or BPD, 81% females. Mentalization was measured by assessment of reflective functioning (RF) from transcripts of the Adult Attachment Interview (AAI). AC was measured by using the Affect Consciousness Interview (ACI). In this mixed PD sample, the RF and AC scores indicated poor functioning and correlations between RF and AC were low to moderately positive. In the PD-specific subgroups, correlations between RF and AC were positive (moderate to high) in the APD group (n = 26), but insignificant in the BPD group (n = 33). In conclusion, the positive relationship between RF and AC may not be generalized to all types of psychopathology. Our results indicate a strong relationship between impaired AC and poor mentalizing capacities among APD patients in particular.