Changes in attachment organization and reflective function (RF) were assessed as putative mechanisms of change in 1 of 3 year-long psychotherapy treatments for patients with borderline personality disorder (BPD). Ninety patients reliably diagnosed with BPD were randomized to transference-focused psychotherapy (TFP), dialectical behavior therapy, or a modified psychodynamic supportive psychotherapy. Attachment organization was assessed with the Adult Attachment Interview and the RF coding scale. After 12 months of treatment, participants showed a significant increase in the number classified secure with respect to attachment state of mind for TFP but not for the other 2 treatments. Significant changes in narrative coherence and RF were found as a function of treatment, with TFP showing increases in both constructs during treatment. No changes in resolution of loss or trauma were observed across treatments. Findings suggest that 1 year of intensive TFP can increase patients' narrative coherence and RF. Future research should establish the relationship between these 2 constructs and relevant psychopathology, identify treatment components responsible for effecting these changes, and examine the long-term outcome of these changes.