Social deficits and emotional dysregulation have been suggested as explanations for the relational difficulties experienced by patients with borderline personality disorder (BPD). The neuropeptide oxytocin (OXT) is a possible neurobiological underpinning of these adversities, and this study examines possible correlations between BPD symptomatology and serum OXT. Thirty-eight female participants (BPD group n = 18, matched control group n = 20) with a mean age of 29.5 years (standard deviation 9.2) were assessed for personality disorders, general psychopathology, childhood trauma and perceived stress. OXT was measured in serum samples. We found no significant difference between patient and control group in terms of OXT levels. However, post hoc analysis showed a relationship in the patient group between civil status and OXT (p < 0.05), indicating higher levels of OXT for patients in a romantic relationship. The idea of OXT as a pro-social love hormone is perhaps too simplistic, and factors like attachment style, exposure to trauma and psychiatric disorders must be considered in order to understand its diverse functions. Contrary to our expectations, we did not find lower serum OXT levels in the BPD group. However, BPD patients in a romantic relationship had higher levels of serum OXT than single BPD patients. Copyright © 2017 John Wiley & Sons, Ltd.