Background: Traditionally, the presence of post-traumatic stress disorder (PTSD) in subjects diagnosed with borderline personality disorder (BPD) has been the object of scant empirical research. The clarification of issues related to the different areas of study for this comorbidity is not only significant from a theoretical point of view but also relevant for clinical practice. The aim of this review is to describe the main theoretical findings and research conclusions about the comorbidity between PTSD and BPD. Methods: A literature review was carried out via PubMed and PsycINFO for the period between 1990 and September 2013. The descriptors used were ‘post-traumatic stress disorder', ‘borderline personality disorder', ‘PTSD', ‘complex PTSD' and ‘BPD'. Results: Epidemiological studies show that the risk of PTSD among BPD subjects is not regularly higher than in subjects with other personality disorders. Furthermore, there is no conclusive evidence about the main aetiopathogenic mechanism of this comorbidity, either of one disorder being a risk factor for the other one or of common underlying variables. Concerning comparative studies, several studies with PTSD-BPD subjects have found a higher severity of psychopathology and psychosocial impairment than in BPD subjects. With regard to nosological status, the main focus of controversy is the validation of ‘complex PTSD', a clinical entity which may comprise a subgroup of PTSD-BPD subjects. With regard to treatment, there are preliminary evidences for the efficient treatment of psychopathology in both PTSD and BPD. Conclusions: These findings are remarkable for furthering the understanding of the link between PTSD and BPD and their implications for treatment. The results of this review are discussed, including methodological constraints that hinder external validity and consistency of referred findings.