Organic personality disorder (OPD) is the traditional diagnostic category used to account for personality disturbances after traumatic brain injury (TBI). The recent use of Axis-II personality disorders, notably borderline personality disorder (BPD), has appeared in the TBI literature as an alternative to OPD. This would presumably offer a better description and understanding of the multiple clinical manifestations of these personality changes and disorders. This article offers a view that it is possible and fruitful to use both diagnoses in a complementary manner. An accurate recognition of the respective phenomenologies of both BPD and OPD is a key factor in achieving a differential diagnosis, including, if required, a dual diagnosis. The phenomenology of both conditions in reference to DSM-IV criteria is compared and illustrated through two clinical vignettes.